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CALIFORNIA  COLLEGE  OF  MEDICINE 


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THE 

INTERVERTEBRAL 
FORAMEN 


SWANBERG 


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THE 

INTERVERTEBRAL 
FORAMEN 


AN  ATLAS  AND  HISTOLOGIC  DESCRIPTION 

OF  AN  INTERVERTEBRAL  FORAMEN 

AND   ITS  ADJACENT  PARTS 


BY 


HAROLD   SWANBERG 

Mtmbtr  American  Association  for  tht  Advancement  of  Science 


WITH  AN  INTRODUCTORY  NOTE 
BY 

PROF.  HARRIS  E.  SANTEE 


Illustrated  by  16  full  page  plates  none  of 
which  have  ever  before  appeared  in  print 


CHICAGO  SCIENTIFIC  PUBLISHING  CO. 

S.  W.  Cor.  Grace  and  Osgood  Streets 
CHICAGO,    ILLINOIS 


COPYRIGHT,  1914 

BY 
HAROLD   SWANBERG 


FY  OF 
LLEGE  OF  OGTEO 


SDeimateti 

To  THE  MEMORY  OP  MY  MOTHER 
LILLIAN  GOERZ  SWANBERG 


OIHT 


INTRODUCTORY  NOTE 

By 

HARRIS  E.  SANTEE,  A.  M.,  Ph.  D.,  M.  D. 

DEPARTMENT  OF  ANATOMY,  JENNER  MEDICAL  COLLEGE  AND  CHICAGO  COL- 
LEGE OF  MEDICINE  AND  SURGERY. 


TAKE  pleasure  in  writing  an  introductory  note  to 
the  monograph  of  Mr.  Harold  Swanberg.  Accurate 
information  is  always  valuable,  and  it  is  such  that  Mr. 
Swanberg  presents.  A  careful  investigation  of  the 
intervertebral  foramina  and  their  contents  is  of  special  interest. 
Though  the  field  is  so  limited,  it  is  sufficiently  broad  to  form 
the  anatomic  basis  for  several  schools  of  practice.  Mr.  Swan- 
berg shows  by  actual  sections  the  exact  relations  of  the  first 
dorsal  nerve  at  the  intervertebral  foramen.  A  study  of  his 
work  will  help  to  determine  whether  compression  of  the 
nerves  at  this  point  is  likely  to  occur;  and  whether,  therefore, 
there  is  substantial  ground  for  the  doctrine  that  such  com- 
pression is  the  immediate  cause  of  all  or  of  a  considerable  num- 
ber of  pathologic  conditions. 


PREFACE 

[HIS  atlas  is  absolutely  unique.  To  the  best  of  the 
author's  knowledge  it  contains  the  first  photomicro- 
graphs and  scientific  description  of  an  intervertebral 
foramen  that  has  ever  been  published.  No  apology 
is  therefore  offered  for  its  appearance.  During  the  past 
quarter  of  a  century  a  great  deal  of  attention  has  been  directed 
to  the  spinal  column  from  a  therapeutical  standpoint.  Many 
systems  have  arisen  claiming  that  the  great  majority  of 
diseases  have  their  origin  from  various  spinal  abnormalities, 
which  result  in  producing  pressure,  or  other  phenomena,  to 
the  nerves  in  the  intervertebral  foramina.  It  is  not  the  pur- 
pose of  this  book  to  discuss  any  of  the  pathologic  changes 
which  take  place  to  the  nerves  or  the  intervertebral  foramina, 
but  to  present  a  clear  and  concise  description  of  the  normal 
histologic  structure  of  this  part,  with  special  reference  to  the 
relations  of  the  nervous  structures.  Once  the  normal  struc- 
ture is  mastered,  the  reader  will  then  be  in  a  better  position 
to  judge  for  himself  the  effects  of  pathologic  changes  to 
these  parts,  and  can  formulate  his  own  opinion  about  nerve 
pressure,  impingement,  irritation,  etc.,  as  a  cause  of  disease. 
It  will  be  interesting  to  note  how  the  photomicrographic 
plates  in  this  book  were  prepared.  First,  photomicrographs 
were  taken  from  the  original  slides.  These  were  then  further 
enlarged  and  carefully  retouched.  The  retouched  photomicro- 
graphs were  then  all.  reduced  to  an  approximately  equal 
diameter  and  half-tone  plates  made.  At  considerable  extra 
expense  the  best  engravers'  proving  paper  was  used  to  repro- 
duce the  plates.  This  renders  the  detail  of  the  plates  as 
distinct  as  it  is  possible  to  be  made,  yet  every  part  is  shown 
exactly  as  it  normally  occurs. 

The  Basle  anatomical  terminology  is  used  throughout,  and 

11 


12  PREFACE 

the  description  of  the  text  is  so  worded  that  the  reader  can 
understand  each  plate  separately  or  follow  them  consecutively. 

The  author  has  been  greatly  interested  in  spinal  therapeu- 
tics for  many  years.  The  plan  of  this  monograph  was  con- 
ceived in  1910,  and  after  much  research  and  microscopic 
examinations  of  various  foramina  the  present  description  was 
written. 

Inasmuch  as  this  work  is  original  and  the  failure,  after 
a  most  careful  search,  to  find  any  literature  on  the  structure 
of  the  intervertebral  foramen,  I  have  had  little  need  to  make 
book  references.  However,  Santee's  "Anatomy  of  the  Brain 
and  Spinal  Cord,"  and  Gray's  "Anatomy,"  have  both  been 
consulted. 

Zan  D.  Klopper,  M.  D.,  of  Chicago,  has  drawn  Plates  1 
and  2,  and  did  the  retouching  of  all  the  photomicrographs.  I 
have  sketched  Plates  3  and  4. 

I  desire  to  express  my  sincere  thanks  to  my  friend  and 
former  associate,  L.  D.  Heigerick,  for  staining  the  original 
sections  and  for  great  aid  rendered  in  the  final  proof-revision ; 
to  J.  C.  Vestergaard  for  much  time  spent  in  securing  the 
photomicrographs;  to  Oakley  Smith  for  encouragement 
early  in  the  work;  to  Professor  Harris  E.  Santee,  M.  D.,  for 
many  valuable  suggestions ;  and  to  my  sister,  Miss  Marion  G. 
Swanberg,  and  my  wife  for  their  valued  assistance  rendered 
in  preparing  and  correcting  the  original  manuscript. 

CHICAGO,  1913.  HAROLD  SWANBERG. 


TABLE  OF  CONTENTS 

t  PAGE 

Introduction   15 

Description  of  Plate    1    20 

Description  of  Plate    2    24 

Description  of  Plate    3    28 

Description  of  Plate    4    32 

Description  of  Plate    5  (Section  35)    38 

Description  of  Plate    6  (Section  33)    45 

Description  of  Plate    7  (Section  31)    50 

Description  of  Plate    8  (Section  2>9)    55 

Description  of  Plate    9  (Section  26)    59 

Description  of  Plate  10  (Section  24)   64 

Description  of  Plate  11  (Section  22J4)    69 

Description  of  Plate  12  ( Section  21)   74 

Description  of  Plate  13  (Section  19)    79 

Description  of  Plate  14  (Section  17)  83 

Description  of  Plate  15  (Section  15)    88 

Description  of  Plate  16  (Section  13)   94 

Summary  98 


13 


LIST  OF  PLATES 

PLATE  PAGE 

1.  First  and  second  dorsal  vertebrae,  with  intervertebral  disc  con- 

necting them,  and  vertebral  extremity  of  right  second  rib  (cat\    21 

2.  First  and  second  dorsal  vertebrae,  with  intervertebral  disc  con- 

necting   them,    and    vertebral    extremity   of    right    second    rib 
(human)  25 

3.  Right  first  dorsal  intervertebral  foramen  and  its  adjacent  bony 

boundaries  (outline  drawing) 29 

4.  Second  dorsal  vertebra  showing  the  spinal  canal  and  its  contents 

(partly  diagrammatic)   33 

5.  Spinal  canal  and  its  adjacent  bony  boundaries  opposite  the  right 

first  dorsal  intervertebral  foramen 39 

6.  Spinal  canal  and  its  adjacent  bony  boundaries  opposite  the  right 

first  dorsal  intervertebral  foramen,  external  to  Plate  5 47 

7.  Spinal  canal  and  its  adjacent  bony  boundaries  opposite  the  right 

first  dorsal  intervertebral  foramen,  external  to  Plate  6 51 

8.  Spinal  canal  and  its  adjacent  bony  boundaries  opposite  the  right 

first  dorsal  intervertebral  foramen,  external  to  Plate  7 57 

9.  Right  first  dorsal  intervertebral  foramen  and  its  adjacent  bony 

boundaries    61 

10.  Immediately  external  to  right  first  dorsal  intervertebral  foramen    65 

11.  External   to   right    first   dorsal   intervertebral    foramen,   external 

to  Plate  10 71 

12.  External   to    right    first   dorsal   intervertebral    foramen,   external 

to  Plate  11 75 

13.  External   to   right   first    dorsal   intervertebral    foramen,   external 

to  Plate  12 81 

14.  External  to   right   first   dorsal   intervertebral    foramen,   external 

to  Plate   13 85 

15.  External   to   right   first   dorsal    intervertebral    foramen,    external 

to  Plate  14 89 

16.  External  to   right   first   dorsal   intervertebral   foramen,  external 

to  Plate  15 95 

14 


INTRODUCTION 


HE  purpose  of  this  book  is  to  present  an  accurate  and 
scientific    description    of    an    intervertebral    foramen 
and  its  adjacent  parts,  with  special  reference  to  the 
relations  of    the    nervous    structures.     The    animal 
chosen  to  furnish  the  necessary  specimen  was  the  cat.* 

ANIMAL.  This  was  an  ordinary  eight-month-old  female 
house  cat  which  was  pregnant  when  secured,  one  kitten  being 
born  on  that  day  and  another  on  the  following  day  when 
she  was  etherized.  A  post-mortem  was  made,  but  no  gross 
abnormal  changes  were  noted.  There  was  a  slight  normal 
congestion  of  the  pelvic  viscera  present,  due  to  the  recent 
pregnancy.  The  cat  measured  about  twenty  inches  from  tip 
of  nose  to  root  of  tail,  this  being  the  ordinary  size.  She  was 
well  built  but  not  stout. 

SPECIMEN.  The  right  first  dorsal  intervertebral  foramen 
was  selected  for  study.  The  right  half  of  the  first  and  second 
dorsal  vertebrae  with  the  vertebral  extremity  (head  and  neck) 
of  the  right  second  rib  attached  was  used  as  the  specimen. 
The  bones  were  sawed  off,  so  that  as  small  an  amount  of 
bone  as  possible  was  present  around  the  intervertebral  fora- 
men. The  specimen  was  placed,  with  the  part  where  the 
spinal  cord  had  been  cut  longitudinally,  on  a  block  and  then 

*This  animal  and  the  human  are  very  similar  from  a  histologic  and  an  anatomical 
standpoint,  and  they  both  possess  a  cerebrospinal  and  sympathetic  nervous  system 
of  similar  arrangement.  Specimens  from  this  animal  are  even  more  desirable  for 
study  than  the  human  because  of  their  small  size  and  of  the  ease  with  which  fresh 
material  can  be  obtained.  The  human  specimens  are  too  large  to  have  sections 
cut  with  the  microtome  suitable  for  microscopic  examination,  and,  in  addition, 
require  too  long  a  time  for  the  bones  to  decalcify,  which  must  be  done  in  order 
to  cut  them.  Each  day  the  specimens  are  in  the  decalcifying  fluid  (nitric  acid), 
the  soft  tissues  are  destroyed  to  a  certain  extent. 

15 


16  THE   INTERVERTEBRAL   FORAMEN 

mounted  in  this  position.  The  sections  were  cut  parallel  to 
the  sagittal  plane.  Such  sections  cut  the  spinal  nerve  trans- 
versely as  it  emerged  from  the  intervertebral  foramen  and 
gave  a  complete  view  of  the  foramen.  Sections,  of  course, 
were  cut  from  without  inward  and  labeled  accordingly. 
Therefore,  Section  1  would  show  structures  completely  ex- 
ternal to  the  intervertebral  foramen,  while  number  60,  the  last 
one,  would  show  structures  inside  the  spinal  canal,  as  the 
spinal  cord.  Sixty  sections  in  all  were  prepared,  each  being 
about  14  microns  (1/1800  of  an  inch)  in  thickness  and  from 
70  to  140  microns  apart.  However,  all  the  sections  are  not 
shown  in  this  text  because  there  would  not  be  enough  change 
between  each.  Photomicrographs  and  descriptions  for  every 
alternate  one  from  numbers  13  to  35,  are  given,  there  being 
twelve  of  them  in  all. 

It  is  extremely  important  that  the  reader  should  under- 
stand just  how  the  specimen  was  cut  if  he  wishes  to  interpret 
the  photomicrographs. 

DESCRIPTION  OF  PLATES.  Plates  1  to  4  show  draw- 
ings which  will  help  the  reader  to  better  understand  the 
photomicrographs  which  follow. 

Plates  5  to  16,  the  remaining  ones,  are  retouched  photo- 
micrographs of  the  intervertebral  foramen  and  its  adjacent 
parts.  Each  plate  corresponds  to  a  section  and  the  plates  are 
enumerated  from  within  outward,  tJiat  is,  reversing  the  order  in 
which  they  were  cut.  Plate  5,  the  first  photomicrograph,  rep- 
resents a  section  inside  the  spinal  canal,  and  Plate  16,  the 
last  one,  represents  a  section  outside  of  the  intervertebral 
foramen.  Since  the  photomicrographs  correspond  to  every 
alternate  section  they  are  from  140  to  280  microns  apart 
(1/180  to  1/90  of  an  inch). 

Arrangement  of  Photomicrographs.  Plates  5,  6,  7  and  8 
(Sections  35,  33,  31,  29)  are  taken  internal  to  the  intervertebral 
foramen,  viz.,  in  the  spinal  (vertebral)  canal. 


INTRODUCTION  17 

Plate  9  (Section  26)  is  in  the  intervertebral  foramen 
proper. 

Plates  10,  11,  12,  13,  14,  15  and  16  (Sections  24,  22#,  21, 
19,  17,  15,  13)  are  external  to  the  intervertebral  foramen. 

Plates  8  and  10  are  so  close  to  the  intervertebral  foramen 
that  they  could  almost  be  considered  as  in  it. 

TECHNIQUE.  The  specimen  was  carefully  dissected, 
all  possible  traumatism  being  avoided.  It  was  put  through 
the  usual  histologic  technique,  using  Orth's  fluid  for  a  fixing 
agent,  nitric  acid  for  decalcification,  alcohol  for  hardening  and 
celloidin  for  mounting.  The  sections  were  stained  with 
(Delafield's)  hematoxylin  and  eosin. 

MEASUREMENTS!  The  metric  system  is  used  in  all  the 
work.  A  micron  (/*)  is  equivalent  to  1/1000  of  1  millimeter, 
(mm.),  or  about  1/25000  of  an  inch.  One  mm.  is  equivalent 
to  about  1/25  of  an  inch. 

THE  SPINAL  NERVE.  The  spinal  nerve  is  formed  by 
the  anterior  or  efferent  (motor)  and  posterior  or  afferent 
(sensory)  roots  which  pass  from  the  spinal  cord. 

Anterior  (Motor)  Root.  The  emergence  is  by  several 
filaments  from  the  antero-lateral  groove  of  the  spinal  cord; 
the  real  origin  being  in  the  anterior  horns  of  the  cord. 

Posterior  (Sensory)  Root.  The  emergence  is  by  sev- 
eral filaments  from  the  postero-lateral  groove  of  the  spinal 
cord;  the  real  origin  being  in  the  ganglion  on  the  posterior 
root.  It  is  larger  in  size  than  the  anterior  root  on  account 
of  there  being  more  sensory  than  motor  nerves  in  the  body. 
It  is  further  distinguished  from  the  anterior  root  by  the 
presence  of  a  ganglion  on  it,  called  the  spinal  ganglion.  The 
spinal  ganglion  is  situated  on  the  posterior  root  just  before 
it  unites  with  the  anterior  root  in  the  spinal  canal  and  is 
located  opposite  to  the  intervertebral  foramen.  (See  Plates  4, 
5,  6  and  7.) 

The  anterior  and  posterior  roots  unite  in  the  spinal  canal 


18  THE   INTERVERTEBRAL  FORAMEN 

or  at  the  junction  of  the  spinal  canal  and  intervertebral  fora- 
men to  form  the  spinal  nerve.  The  nerve  passes  through  the 
intervertebral  foramen,  and  after  emerging  from  it  completely, 
bifurcates  into  an  anterior  and  a  posterior  primary  division. 
The  anterior  primary  division  is  by  far  the  larger,  for  it  is  the 
one  which  helps  form  the  various  plexuses  to  supply  the 
muscles  and  skin  of  the  arm,  leg,  etc.  The  posterior  primary 
division  is  smaller  for  it  supplies  only  a  few  spinal  muscles 
and  a  little  skin  over  the  spine.  The  spinal  nerve  contains 
sensory  and  motor  fibers  and  gives  off  both  fibers  to  its 
anterior  and  posterior  divisions.  There  are,  however,  a  few 
exceptions  to  this  arrangement. 

SYMPATHETICS.  Like  the  spinal  nerves,  the  sym- 
pathetics  consist  of  two  kinds  of  fibers — efferent  (vasomotor, 
secretory,  etc.)  and  afferent  (sensory).  The  efferent  fibers 
arise  in  the  lateral  horn  of  gray  matter  in  the  spinal  cord, 
pass  out  in  the  anterior  root  and  then  into  the  spinal  nerve. 
Here  they  unite  with  the  afferent  fibers  which  take  origin 
from  the  spinal  ganglion  on  the  posterior  root  of  the  spinal 
nerve.  The  efferent  and  afferent  fibers  then  pass  together 
into  the  anterior  primary  division  of  the  spinal  nerve.  Leaving 
this,  they  form  the  white  rami  communicantes,  and  pass  to  the 
ganglion  of  the  sympathetic  cord  in  this  situation.  Sym- 
pathetic fibers  also  pass  from  the  ganglion  of  the  sympathetic 
cord  back  to  the  spinal  nerve.  These  are  called  gray  rami 
communic antes.  They  accompany  the  white  rami  and  join  the 
anterior  primary  division.  Gray  rami  pass  to  every  spinal 
nerve  and  accompany  its  various  divisions.  Every  cranial 
nerve  also  has  a  sympathetic  connection,  but  those  fibers 
which  pass  to  them  are  not  called  gray  rami,  yet  they  are 
similar  to  them.  White  rami,  however,  are  only  derived  from 
the  first  dorsal  to  second  lumbar  nerves  (inclusive),  and  from 
the  second,  third,  and  fourth  sacral  nerves.  The  sympathetic 


INTRODUCTION  19 

fibers  that  pass  through  the  intervertebral  foramen  are  in  the 
substance  of  the  spinal  nerve. 

The  photomicrographs  in  this  text  show  the  following 
nervous  structures : 

1.  Anterior  and  posterior  roots ;  spinal  ganglion  on  pos- 
terior root; 

2.  Spinal  nerve; 

3.  Anterior   and   posterior   primary   divisions; 

4.  White  and  gray    rami    communicantes    of    the    sym- 
pathetic. 

Sympathetic  fibers  are,  no  doubt,  present  in  the  spinal 
nerve  and  its  divisions  as  shown  in  these  plates,  but  they 
cannot  be  distinguished  from  the  other  nerve  fibers.  How- 
ever, white  rami  leaving  and  gray  rami  entering  the  anterior 
primary  division  of  the  spinal  nerve  are  shown.  (See  Plate 
15.)  They  accompany  one  another  and  are  very  closely  asso- 
ciated, being  separated  by  only  a  very  small  amount  of  fibrous 
tissue.* 


*These  findings  agree  with  those  of  Langley,  who  writes  in  Schafer's  Physiology, 
"The  uppermost  thoracic  white  and  grey  rami  are  too  closely  associated  to  be  cut 
separately." 


DESCRIPTION  OF  PLATE  1 


This  plate  shows  the  first  and  second  dorsal  vertebrae, 
with  the  intervertebral  disc  connecting  them,  and  the  vertebral 
extremity  of  the  right  second  rib  of  the  cat.  It  is  enlarged 
three  diameters,  therefore  is  about  the  same  size  as  the  human 
vertebrae.  The  first  dorsal  intervertebral  foramen  is  located 
between  the  first  and  second  dorsal  vertebrae.  The  boundaries 
of  the  foramen  are  shown  and  labeled  in  descriptive  terms 
of  human  anatomy. 

The  Boundaries  of  Right  First  Dorsal  Intervertebral  Foramen 

Body  of  first  dorsal   (above). 

Head  of  second  rib  (below  body). 

(The  external  lateral  part  of  the  intervertebral  disc 
also  forms  an  anterior  boundary,  but  this  is  not 
shown  here,  it  being  internal  to  the  head  of  the 
rib.) 


Anterior 


Posterior J   ^n^erior  articular  process  of  first  dorsal   (above). 
(   Superior  articular  process  of  second  dorsal  (below). 

Superior  {    Pedicle  of  first  dorsal. 
Inferior    {    Pedicle  of  second  dorsal. 

The  boundaries  of  this  intervertebral  foramen  are  the  same 
as  in  the  human  spine.  Only  the  head  and  neck  of  the  rib 
are  shown  here,  the  remaining  part  having  been  sawed  off. 
The  head  of  the  rib  is  the  only  part  of  that  bone  which  helps 
to  form  the  anterior  boundary  of  the  foramen,  the  neck  being 
too  far  external. 

20 


PLATE  1 


A  right  lateral  view  of  the  first  and  second  dorsal  vertebrae, 
with  the  intervertebral  disc  connecting  them,  and  the  vertebral 
extremity  (head  and  neck)  of  the  right  second  rib  of  the  cat, 
(3  diameters.) 


A — Inferior    artici: 

dorsal. 

B— Pedicle    of  first  dorsal. 
C — Body   of  first   dorsal. 
D — Intervertebral    disc. 


ocess    of    first 


E- — Head  and   neck  of   second  rib. 
F — Pedicle   of   second   dorsal. 
G — Superior    articular    process    of    sec- 
ond   dorsal. 


DESCRIPTION   OF   PLATE   1  23 

The  first  and  second  dorsal  vertebrae  of  the  cat  almost 
correspond  with  the  same  vertebrae  in  the  human,  having  the 
same  general  shape  and  arrangement.  They  differ,  however, 
in  the  cat  as  follows:  (1)  The  spinous  processes  are  much 
longer.  (2)  The  transverse  processes  are  in  front  of  the 
articular  processes.  (3)  The  superior  articular  processes  face 
backward  and  inward.  (4)  The  inferior  articular  processes 
of  the  first  dorsal  faces  forward  and  outward. 

The  same  anatomical  directions  are  used  here  and  through- 
out the  text  as  in  the  human,  although  they  should  be  differ- 
ent. For  example :  In  the  human  spine,  the  bodies  of  the 
vertebrae  are  anterior  to  the  spinous  processes,  but  the  cat, 
being  a  quadruped,  the  bodies  of  the  vertebrae  are  inferior 
to  the  spinous  processes.  However,  it  was  thought  best  to 
use  the  same  anatomical  directions  as  in  the  human  so  as  to 
avoid  confusion. 


DESCRIPTION  OF  PLATE  2 

This  shows  the  first  and  second  dorsal  vertebrae  with  the 
intervertebral  disc  connecting  them  and  the  vertebral  ex- 
tremity of  the  right  second  rib  in  the  human.  It  is  life  size 
and  is  shown  in  the  same  position  and  view  as  Plate  1.  It 
gives  an  excellent  idea  of  how  similar  these  bones  are  with 
those  in  the  cat,  the  intervertebral  foramen  of  both  (right 
first  dorsal)  having  the  same  boundaries.  (See  Plate  1.) 


24 


PLATE  2 


A  right  lateral  view  of  the  first  and  second  dorsal  vertebrae, 
with  the  intervertebral  disc  connecting  them,  and  the  vertebral 
extremity  (head  and  neck)  of  the  right  second  rib,  of  the 
human.  (Life  size.) 


A— Inferior    articular    proc 

dorsal. 

B — Pedicel    of   first   dorsal. 
C — Body  of  first   dorsal. 
D — Intervertebral    disc. 


>ss    of    first  E — Head  and   neck   of   second  rib. 

F — Pedicle   of   second   dorsal. 
G — Superior    articular    process    of    sec- 
ond  dorsal. 


DESCRIPTION  OF  PLATE  3 

This  plate  is  an  outline  drawing  of  Plate  9  and  shows  the 
right  first  dorsal  intervertebral  foramen  and  its  adjacent  bony 
boundaries.  It  is  enlarged  13  diameters,  therefore,  is  about 
four  times  the  size  of  the  human.  The  foramen  is  somewhat 
quadrilateral  in  shape,  has  the  same  bony  boundaries,  and  is 
shown  in  the  same  position  as  Plates  1  and  2.  The  foramen 
measures  approximately  4  mm.  (1/6  of  an  inch)  in  its  greatest 
antero-posterior  and  supero-inferior  diameters.  The  darkened 
areas  represent  the  hyaline  articular  cartilage. 

The  Articular  Cartilage  on  Bony  Boundaries 

1.  The  inferior  articular  process  of  the  first  dorsal. 

2.  The  superior  articular  process  of  the  second  dorsal. 

3.  The  body  of  the  first  dorsal. 

4.  The  body  of  the  second  dorsal. 

5.  The  head  of  the  second  rib. 

The  cartilage  is  placed  on  the  articular  processes,  where 
they  articulate  with  one  another,  and  on  the  bodies  of  the 
vertebrae  and  head  of  rib  where  they  articulate.  It  averages 
about  230  microns  (1/110  of  an  inch)  in  thickness  on  the 
articular  processes.  The  first  dorsal  spinal  nerve  is  shown  in 
the  center  of  the  foramen.  It  measures  2.95  by  1.4  mm. 
(1/8x1/18  of  an  inch),  is  oval  in  shape,  and  is  situated 
obliquely  in  the  middle  of  the  foramen.  It  occupies  about  one- 
third  of  the  total  area  of  the  foramen  and  is  not  in  contact 
with  bone  at  any  place.  It  is  closest  to  bone  at  its  antero- 
superior  part,  where  it  is  300  microns  (1/80  of  an  inch)  from 


PLATE  3 


A  right  lateral  view  of  the  right  first  dorsal  intervertebral 
foramen,  with  its  adjacent  bony  boundaries,  and  the  position 
and  size  of  the  right  first  dorsal  spinal  nerve.  (Drawn  from 
Plate  9 — 13  diameters.) 


DESCRIPTION    OF   PLATE   3  31 

the  pedicle  of  the  first  dorsal.  The  long  diameter  of  the  nerve 
runs  from  the  antero-superior  to  the  postero-inferior  part  of 
the  foramen.  The  other  structures  in  the  foramen,  fat  cells, 
fibrous  tissue,  and  blood  vessels,  are  shown  in  the  photomicro- 
graphic  plates. 


DESCRIPTION  OF  PLATE  4 

This  shows  the  second  dorsal  vertebra  with  its  spinal 
canal  and  contents.  It  is  diagrammatic  and  is  enlarged  six 
diameters  so  is  about  twice  the  size  of  the  human.  The  sizes 
of  the  vertebra,  spinal  canal,  and  spinal  cord  are  correct  pro- 
portionally. The  spinal  membranes,  the  spinal  nerve  and  its 
divisions  are  shown  diagrammatically.  The  plate  is  shown  as 
if  one  were  looking  down  upon  the  cord  at  this  level,  and  the 
first  dorsal  spinal  nerve  is  seen  passing  above  the  pedicle  of 
the  second  dorsal  vertebra. 

The  Boundaries  of  Spinal  Canal  (at  This  Level) 

f  Body  of  second  dorsal — (the  posterior  longitudinal 
1        ligament  is  attached  to  its  posterior  surface). 

Lateral     j  Pedicle  of  second  dorsal. 

{Articular  processes  of  second  dorsal,  laterally. 
Laminae  of  second  dorsal,  medially  (the  ligamen- 
tum  flava  is  attached  to  their  anterior  surface). 

The  above  boundaries  are  the  same  as  in  the  human.  The 
canal  is  almost  circular  in  shape,  and  the  spinal  cord  which 
has  nearly  the  same  shape,  is  situated  in  the  center,  occupying 
half  the  space.  The  size  of  the  canal  at  this  level  is  8x6^ 
mm.  and  the  cord  about  4x3^4  mm. 

The  cord  is  surrounded  by  the  pia  mater,  a  thin  membrane, 
which  is  intimately  adhered  to  it,  and  which  dips  down  into 
the  anterior  median  fissure  of  the  cord. 

External  to  the  pia,  the  arachnoid  is  present;  it  is  the 
thinnest  of  the  cord  membranes  and  is  held  in  contact  to  the 
pia  by  trabeculae  of  delicate  connective  tissue  fibers  called 
the  subarachnoid  reticulum.  In  the  recent  state,  this  reticu- 


PLATE  4 


A  transverse  section  of  the  second  dorsal  vertebra  showing 
the  spinal  (vertebral)  canal  and  its  contents.  Partly  diagram- 
matic. (6  diameters.) 


A — Epidural  space  filled  with  fat  cells. 
B — Anterior    median    fissure    of    spinal 

cord. 
C — Fibrous  tissue   connecting  dura  and 

post.  long,   ligament. 
D— Posterior   longitudinal    ligament. 

F~'Spinal0nerve^ 
G — Epineurium. 

H — White  and  gray  rami  of  the  sympa- 
thetic. 

nerve. 
J — Posterior      primary      divisions       of 

spinal    nerve. 
K — Spinal    ganglion. 
L — Posterior    root. 


M— Fibrous     tissue     uniting     the     two 

roots. 

N — Subdural  space. 
O — Fibrous     tissue      fibers       connecting 

dura   with   arachnoid. 
P — Septum   posticum. 
O — Ligamentum    flava. 
R — Arachnoid. 
S — Subarachnoid        space        containing 

arachnoid  reticulum. 
T — Pia   mater. 

U — Periosteum    lining   spinal   canal. 
V — Ligamentum   denticulatum. 
W — Dura  mater. 

All  the  fibrous  tissue  is  shown  in  red. 
The  two  vertical  lines  indicate  the  ex- 
tent of  sections  shown  in  the  photo- 
micrographic  plates  which  follow. 


DESCRIPTION   OF   PLATE  4  35 

lum  is  distended  and  the  space  between  the  arachnoid  and 
pia  is  spoken  of  as  the  subarachnoid  space.  It  contains  a  con- 
siderable amount  of  cerebro-spinal  fluid  and  a  number  of 
blood  vessels.  Opposite  the  posterior  median  groove,  the 
subarachnoid  space  is  practically  subdivided  by  a  longitudinal, 
membranous,  fenestrated  partition  called  the  septum  posticum 
which  connects  the  arachnoid  with  the  pia.  The  arachnoid 
is  really  the  external  layer  of  the  pia.  The  two  membranes 
can  be  separated  only  with  difficulty,  and  could  therefore  be 
considered  as  one,  the  pia-arachnoid. 

External  to  the  arachnoid  we  find  the  dura  mater.  This 
is  the  thickest  of  the  membranes.  It  is  separated  from  the 
arachnoid  by  a  clear  space  called  the  subdural  space.  This 
space  contains  a  few  trabeculae  of  connective  tissue  which 
connect  it  to  the  arachnoid  here  and  there,  and  just  enough 
cerebrospinal  fluid  to  moisten  the  surface.  Outside  of  the 
dura,  and  between  it  and  the  bony  margin  of  the  spinal  canal, 
we  find  a  very  large  space  called  the  epidural  space.  It  con- 
tains mostly  fat,  together  with  blood  vessels  and  some  fibrous 
connective  tissue  fibers.  These  last  are  seen  in  the  anterior 
part,  helping  to  support  the  dura  and  running  from  this 
membrane  to  the  posterior  longitudinal  ligament. 

In  the  above  description,  nothing  has  been  mentioned  of 
the  ligamentum  denticulata.  These  are  folds  of  pia  which 
extend  from  the  lateral  part  of  the  cord  to  the  inner  side  of 
the  lateral  part  of  the  dura  mater,  in  the  interval  between 
the  spinal  nerves,  and  push  the  arachnoid  before  them.  At 
the  level  of  the  spinal  nerves  they  do  not  reach  the  dura  but 
are  free  (as  in  this  plate).  They  divide  the  subarachnoid  and 
subdural  spaces  into  two  parts,  and  separate  the  anterior  and 
posterior  roots  of  the  spinal  nerve  from  one  another.  They 
also  help  to  support  the  cord. 

The  anterior  and  posterior  nerve  roots  pass  horizontally 
lateral  from  their  respective  emergences  at  the  antero- 


36  THE   INTERVERTEBRAL   FORAMEN 

lateral  and  postero-lateral  grooves,  to  the  mid-lateral  side  of 
the  cord.  They  are  invested  in  their  course  by  the  pia  mater 
which  is  really  continuous  on  them  from  the  cord.  The  arach- 
noid also  invests  the  roots  but  only  as  far  as  where  they  pierce 
the  dura  mater.  The  two  roots  at  the  mid-lateral  part  of  the 
cord  pierce  the  dura  separately,  and  this  membrane  passes 
onto  and  covers  them.  However,  the  dura  which  covers  the 
roots  is  by  no  means  as  thick  as  that  which  invests  the  cord. 
Both  the  pia  and  dura  continue  out  on  the  roots,  the  spinal 
nerve  and  its  divisions,  and  form  the  epineurium  of  all  the 
peripheral  nerves. 

After  the  two  roots  pierce  the  dura  separately,  they  are 
held  closely  together  by  fatty-fibrous  tissue.  They  then  pass 
through  the  epidural  space  and  are  entirely  surrounded  by  fat. 
The  posterior  root,  just  before  it  unites  with  the  anterior  root, 
and,  while  it  is  in  the  spinal  canal  immediately  internal  to 
the  intervertebral  foramen,  has  an  enlargement  developed  on 
it — the  spinal  ganglion.  Immediately  after  leaving  the  gan- 
glion, the  two  roots  coalesce,  forming  the  spinal  nerve.  This 
passes  through  the  intervertebral  foramen,  and  after  emerg- 
ing from  it  completely,  bifurcates  into  a  large  anterior  and 
several  small  posterior  primary  divisions.  From  the  anterior 
primary  division  the  white  rami  of  the  sympathetic  leave  and 
the  gray  rami  enter.  The  fat  that  is  present  in  the  epidural 
space  passes  into  the  intervertebral  foramen  and  almost  en- 
tirely surrounds  the  nerve  in  this  situation. 

The  space  between  the  two  vertically  drawn  lines  in  the  plate 
shows  the  extent  of  structures  as  shown  in  the  photomicro graphic 
plates  which  follow.  The  vertical  line,  inside  the  spinal  canal, 
cutting  the  anterior  and  posterior  roots  corresponds  to  Plate  5 
(Section  85).  The  vertical  line,  outside  of  the  intervertebral 
foramen,  cutting  the  anterior  and  posterior  primary  divisions, 
and  the  white  and  gray  rami  of  the  sympathetic  corresponds  to 
Plate  16  (Section  18). 


DESCRIPTION    OF   PLATE    4 


37 


SUMMARY  OF  SPACES  AND  MEMBRANES 
IN  SPINAL  CANAL 


Subarachnoid 

Subdural  Space 

Epidural   Space 

§ 

o 

u 

Space 

1 
PQ 

C 

Fibrous     tissue 

Fat    cells     (abun- 

^_. 

"e3 

<S) 

Subarachnoid     re- 

(small  amount). 

dant). 

c 

ticulum. 

^  & 

•—  '    3 

in 

Cerebrospinal  fluid 

Fibrous     tissue 

ll 

.5 

Cerebrospinal  fluid 

•d 

(small  amount). 

u 

-M 

(anteriorly). 

fr-g 

S 

(abundant). 

| 
(j 

Ligamentum  den- 

1 

Blood  vessels. 

"o   o, 

I 

Blood  vessels. 

2 

ticulata. 

3 

^ 

rt 

^ 

Q 

Anterior  and  pos- 

en   V 

* 

Septum  posticum. 

terior  roots. 

0    « 

O 
o 

Ligamentum    den- 

Spinal  ganglion  on 

I 

ticulata. 

posterior  root. 

••* 

c 

c 

'On 

rt 

C/) 

^ 

G 

0 

PQ 

DESCRIPTION  OF  PLATE  5  (SECTION  35) 

This,  and  all  of  the  following  plates  are  photomicrographs  of  the  right  first 
dorsal  interyertebral  foramen  and  its  adjacent  parts.  Each  is  seen  in  a  right  lateral 
view,  and  is  enlarged  approximately  13  diameters. 

This  is  the  most  internal  plate  of  the  series  and  shows 
the  spinal  canal  and  its  adjacent  bony  boundaries  opposite 
the  right  first  dorsal  intervertebral  foramen.  It  is  really  in 
the  epidural  space,  that  is,  the  space  between  the  dura  mater 
and  the  bony  walls  of  the  spinal  canal.  It  is  cut  in  the  same 
manner  as  Plate  3,  except  that  it  is  internal  to  this  plate. 
However,  the  same  general  directions  that  were  given  in  con- 
nection with  the  above  will  apply  to  this  plate.  The  anterior, 
posterior,  superior  and  inferior  directions  are  labeled  on  the 
plate  as  well  as  the  bony  boundaries.  On  passing  internal 
from  here  far  enough,  the  spinal  cord  is  encountered  and  pass- 
ing external  a  short  distance,  the  intervertebral  foramen  is 
entered. 

The  Bony  Boundaries  of  Spinal  Canal   (as  Shown  in  This 
Plate) 


/Body  of  first  dorsal  (above). 


Anterior  J  Head  of  second  rib   (middle). 
I^Body  of  second  dorsal  (below). 

Inferior   articular   process   of     the     first     dorsal 
(above). 


Posterior 


Superior  articular  process   of  the   second   dorsal 

(below). 
(These  are  held  together  by  part  of  the  capsular 

ligament  which  can  be  seen  in  the  canal.) 

Part   of   the   interarticular  ligament   of   the   costo-central 
articulation  is  seen  attached  to  the  posterior  surface  of  the 

38 


PLATE    5    (Section    35) 


39 


(Superior) 


(Anterior) 


Superior 

Articular 

Process 


(Inferior) 


A  right  lateral  view  of  the  spinal  canal  and  its  adjacent 
bony  boundaries  opposite  the  right  first  dorsal  intervertebral 
foramen. 


A — Foreign    particles. 
B — Unknown    particle. 
C— Blood  vessel. 
D — Vacant   space. 

•p p          .          •          V  ,  f 

(spinal   ganglion). 
F — Capsular    ligament. 
G — Blood   vessels. 
H— Articular  cartilages. 

I — Blood  vessel. 

J — Foreign  particles. 


K — Blood  vessel. 

L, — Vacant  space. 

M — Voluntary  muscle. 

N— Blood  vessel. 

O — Filaments      of      anterior      root      of 

spinal   nerve. 
P — Fatty-fibrous  tissue. 

r  Blood    vessel    (greatly    distended). 
Articular   cartilages. 
S — Fibrous  tissue    (dense). 
T — Interarticular  ligament. 
U — Articular  cartilages. 
V— Fat  cells. 


DESCRIPTION   OF   PLATE  5  41 

head  of  the  rib.    The  most  internal  part  of  each  articular 
process  is  the  part  present. 

The  reason  that  no  bony  boundaries  are  shown  superiorly 
or  inferiorly  is  because  this  section  is  in  the  spinal  canal. 
Passing  externally  a  short  distance  and  entering  the  inter- 
vertebral  foramen,  the  pedicle  of  the  first  dorsal  is  found 
above  and  the  pedicle  of  the  second  dorsal  below.  All  the 
bone  present,  in  this  and  the  following  plates,  is  of  a  cancel- 
lous  nature,  covered  with  an  outer  layer  of  compact  bone 
which  is  typical  of  the  vertebrae  and  ribs. 

The  Articular  Cartilage  on  Bony  Boundaries. 

1.  Inferior   articular    process   of   first   dorsal. 

2.  Superior  articular  process  of  second  dorsal. 

3.  Body  of  first  dorsal. 

4.  Body  of  second    dorsal. 

5.  Head  of  second  rib. 

Hyaline  cartilage  is  seen  on  the  above  parts  where  the 
bones  articulate.  (In  this  plate  there  is  a  very  small  amount 
on  the  articular  processes,  but  considerable  on  the  bodies  of 
the  vertebrae  and  head  of  rib.) 

Centering  all  efforts  on  the  spinal  canal  itself,  i.  e.,  the 
space  between  the  bony  boundaries,  the  structures  outside  of 
the  canal  will  not  be  considered. 


The  Contents  of  Spinal  Canal  (as  Shown  in  This  Plate) 

1.  Nervous  Structures.  5.  Vacant  Spaces. 

2.  Fat  Cells.  6.  Foreign  Particles 

3.  Blood   Vessels.  7.  Unknown  Particle. 

4.  Fibrous  Tissue. 


42  THE    INTERVERTEBRAL   FORAMEN 

1.    Nervous  Structures. 

Anterior  and  posterior  roots  (spinal  ganglion  on  posterior 
root) . 

The  two  large  structures  in  about  the  center  of  the 
canal  are  the  anterior  and  posterior  nerve  roots.  They  are 
posterior  to  the  lower  part  of  the  body  of  the  first  dorsal 
and  are  cut  transversely.  They  are  connected  by  fatty-fibrous 
tissue  and  are  situated  freely  in  the  canal,  being  intimately 
surrounded  by  fat  cells  and  vacant  spaces.  The  roots  have 
these  same  relations  in  the  plates  which  follow.  The  anterior 
root  consists  of  two  separate  filaments,  each  being  surrounded 
by  fibrous  tissue.  There  are  no  nerve  cells  in  either  of  the 
filaments.  A  small  blood  vessel  is  seen  in  the  fibrous  tissue 
separating  them.  The  posterior  root  consists  of  a  single  fila- 
ment, is  larger,  and  is  made  up  entirely  of  the  posterior  root 
ganglion  (spinal  ganglion)  in  this  plate,  for  under  high  power 
magnification  it  shows  numerous  nerve  cells.  The  ganglion 
is  surrounded  by  fibrous  tissue.  The  fibrous  tissue  which 
surrounds  the  nerves  is  derived  from  the  dura  and  pia  of  the 
cord  and  is  known  as  the  epineurium. 

2.  Fat  Cells. 

The  canal  is  almost  entirely  filled  with  them. 

They  form  the  main  composition  of  the  canal.  They  are 
all  typical  in  structure  and  the  nervous  structures  are  em- 
bedded in  them.  Running  throughout  the  fat,  very  fine 
strands  of  fibrous  tissue  are  found  here  and  there.  Passing 
externally  the  fat  cells  gradually  become  less  in  number. 

3.  Blood  Vessels 

(1)  Large  distended  one  posterior  to  head  of  rib  (largest). 

(2)  A  small  one  in  capsular  ligament  (distended). 

(3)  One  of  fair  size  posterior    to    body    of    first    dorsal 
(distended). 


DESCRIPTION   OF   PLATE   5  43 

(4)  One  of  fair  size  anterior  to  inferior  articular  process  of 
first  dorsal   (distended). 

(5)  Two  small  ones  in  fat  tissue  inferior  to  nervous  struc- 
tures (collapsed). 

(6)  A  very  small  one  between  the  two  filaments  of  ante- 
rior root. 

The  vessels  are  very  numerous.  The  dark  substance  seen 
occasionally  in  their  lumen  throughout  the  plates  is  blood. 
No  attempt  has  been  made  to  distinguish  the  arteries  from 
the  veins. 

4.  Fibrous  Tissue. 

(1)  Forming  the  epineurium  of  nervous  structures. 

(2)  Forming  the  walls  of  blood  vessels. 

(3)  Very  fine  fibers  among  the  fat  cells. 

(4)  Forming  the  periosteum  of  all  the  bones. 

(5)  Forming  the  internal  part  of  the  capsular  ligament 
connecting  the  articular  processes   (dense). 

(6)  A  small  amount  posterior  to  head  of  rib  (dense). 

(7)  Uniting  the  anterior  and  posterior  roots  (fine). 
The  fibrous  tissue  is  not  very  abundant  in  amount.     The 

first  four  of  the  above  occur  throughout  the  plates,  so  will  not 
be  repeated.  Passing  externally  the  fibrous  tissue  steadily  in- 
creases in  amount. 

5.  Vacant  Spaces. 

(1)  Anterior  and  superior  to  anterior  root. 

(2)  Posterior  to  posterior  root. 

These  are  spaces  where  all  tissue  is  absent.  They  are 
sometimes  difficult  to  distinguish  from  blood  vessels.  How- 
ever, in  the  case  of  a  blood  vessel  the  walls  are  thick  and 
have  the  structure  of  a  vessel.  These  spaces  are,  no  doubt, 
due  to  faulty  technic,  for  there  are  normally  no  vacant  spaces 
in  the  tissues.  They,  no  doubt,  represent  areas  where  the  fat 


44  THE   INTER  VERTEBRAL   FORAMEN 

cells  have  been  washed  out.     They  appear  at  various  situa- 
tions in  the  plates  which  follow. 

6.  Foreign  Particles. 

(1)  In  the  superior  part  of  canal. 

(2)  In  the  inferior   part  of  canal. 

These  consist  mainly  of  irregularly  scattered  splinters  of 
bone,  due  to  the  sawing  that  was  necessary  to  secure  the 
specimen. 

7.  Unknown  Particle. 

Posterior  and  superior  to  posterior  root. 
It  evidently  belongs  to  the  nervous  structure,  for  it  be- 
comes continuous  with  them   internally. 


DESCRIPTION    OF   PLATE   6    (Section   33) 

This  shows  the  spinal  canal  and  its  adjacent  bony  boun- 
daries external  to  Plate  5. 

The  Bony  Boundaries  of  Spinal  Canal 

Similar  to  the  former  plate  (Plate  5) 

Inferiorly,  the  pedicle  of  the  second  dorsal  is  beginning 
to  form  and  this  nearly  fills  the  canal  there.  The  head  of  the 
rib  is  more  bony  in  composition.  In  the  former  plate  it  was 
mostly  cartilaginous,  which  was  due,  no  doubt,  to  the  presence 
of  the  extreme  internal  part  of  the  head  of  the  rib.  This  part 
is  covered  with  hyaline  cartilage  and  articulates  with  the  in- 
tervertebral  disc.  Naturally,  passing  externally,  the  cartilage 
gradually  disappears,  and  bone  takes  its  place.  More  of  the 
articular  processes  can  be  seen  in  this  plate,  because  of  the 
fact  that  their  most  internal  parts  were  shown  in  the  former 
plate.  The  body  of  the  first  dorsal  is  smaller  antero- 
posteriorly.  This  is  due  to  the  lateral  sides  of  the  vertebrae 
eventually  terminating  in  a  ridge.  The  canal  is  not  so  wide 
superiorly.  The  same  reason  which  explained  the  change  in 
the  inferior  part  will  also  apply  here.  The  spinal  canal  is 
oval  in  shape  like  the  bodies  of  the  vertebrae  when  cut  trans- 
versely. As  the  canal  passes  laterally  it  becomes  smaller 
in  an  antero-posterior  direction,  therefore  it  appears  smaller 
in  this  plate  than  in  the  former.  The  interarticular  ligament 
is  smaller. 

To  sum  up  these  bony  changes : 

1.  The  pedicle  of  second  dorsal  is  beginning  to  form. 

2.  The  inferior  part  of  canal    is    smaller    in    an    antero- 
posterior  diameter. 

45 


46  THE    INTERVERTEBRAL   FORAMEN 

3.  The  head  of  rib  is  more  bony  in  its  composition. 

4.  The  articular  processes  are  larger. 

5.  The  body  of  first  dorsal  is  smaller  in  an  antero-posterior 
diameter. 

6.  The  superior  part  of  canal   is  smaller  in  an  antero- 
posterior  diameter. 

The  Articular  Cartilage  on  Bony  Boundaries 

Similar  to  the  former  plate  (Plate  5) 

The  Contents  of  Spinal  Canal 

Similar  to  the  former  plate  (Plate  5) 

1.  Nervous  Structures. 

Anterior  and  posterior  roots  (spinal  ganglion  on  posterior 
root). 

These  roots  are  situated  in  about  the  same  position,  but 
appear  closer  together,  less  fatty-fibrous  tissue  separating 
them.  The  epineurium,  surrounding  the  superior  filament  of 
the  anterior  root,  appears  slightly  torn,  due,  no  doubt,  to 
faulty  technic. 

2.  Fat  Cells. 

The  canal  is  almost  entirely  filled  with  them. 
They  are  less  in  number  on  account  of  the  smaller  size 
of  the  canal. 

3.  Blood  Vessels. 

(1)  Large  distended  one  posterior  to  head  of  rib  (largest). 

(2)  One  of  fair  size  in  capsular  ligament  (distended). 

(3)  One  of  fair  size  posterior  to    body    of    first    dorsal 
(distended). 

(4)  A  small  one  anterior  to  inferior  articular  process  of 
first  dorsal  and  capsular  ligament  (collapsed). 


PLATE    6    (Section    33) 


47 


A  right  lateral  view  of  the  spinal  canal  and  its  adjacent 
bony  boundaries  opposite  the  right  first  dorsal  intervertebral 
foramen,  immediately  external  to  Plate  5. 


A — Foreign  particles. 
B — Unknown  particle. 
C — Posterior  root  of  spinal 

(spir.al    ganglion). 
D — Blood    vessel. 
K — Capsular    ligament. 
F — Blood   vessel. 
G — Articular    cartilages. 
H— Fat  cells. 


I — Blood   vessel. 

J— Voluntary  muscle. 

K — Vacant  spaces. 

L — Filaments      of      anterior      root      o 

spinal    nerve. 
M — Fatty-fibrous    tissue. 
N — Blood    vessel    (greatly    distended). 
O — Articular  cartilages. 
P — Fibrous    tissue    (dense). 
Q— Articular    cartilages. 


DESCRIPTION   OF   PLATE   6  49 

The  large  vessel  is  seen  as  it  passes  posteriorly  in  the 
canal  toward  the  capsular  ligament.  This  vessel  is  larger 
than  normal  on  account  of  it  having  folded  at  its  superior  part, 
due  to  faulty  technic.  Some  fat  cells  can  be  seen  in  its  lumen 
in  this  area.  The  vessel  which  was  in  the  anterior  root 
and  those  in  the  fat  tissue  inferior  to  the  nervous  structures 
have  disappeared.  They,  no  doubt,  became  continuous  with 
the  large  vessel.  The  vessel  anterior  to  the  inferior  articular 
process  in  the  former  plate,  has  descended  somewhat  and  now 
lies  partly  anterior  to  that  part  and  partly  anterior  to  the 
capsular  ligament.  It  may  become  continuous  with  the  vessel 
in  the  ligament,  for  it  appears  smaller  than  in  the  former  plate. 

4    Fibrous  Tissue. 

(1)  The  capsular  ligament  (dense). 

(2)  Posterior  to  head  of  rib  (dense). 

(3)  Uniting  the  anterior  and  posterior  roots   (fine). 
Practically  as  in  the  former  plate,  but  as  a  whole,  slightly 

increased  in  amount.  The  capsular  ligament  is  more  prom- 
inent. The  tissue  posterior  to  the  head  of  the  rib  more 
abundant. 

5.  Vacant  Spaces. 

(1)  Anterior  to  anterior  root. 

(2)  Superior  to  posterior  root. 

6.  Foreign  Particles. 

In  the  superior  part  of  canal. 

They  are  becoming  less  in  number  and  have  entirely  dis- 
appeared in  the  inferior  part. 

7.  Unknown  Particle. 

Posterior  and  superior  to  posterior  root. 
It  has  almost  entirely  disappeared.     This  and  the  former 
plate  are  the  only  ones  in  which  it  is  seen. 


DESCRIPTION   OF   PLATE   7    (Section   31) 

This  shows  the  spinal  canal  and  its  adjacent  bony  boun- 
daries external  to  Plate  6. 

The  Bony  Boundaries  of  Spinal  Canal 

f  Body  of  first  dorsal  (above). 
>r  {  Head  of  second  rib  (below). 

C Inferior  articular  process  of  first  dorsal   (above). 
Posterior  J  Superior  articular  process  of  second  dorsal   (be- 
(^     low). 

Inferior      {Pedicle  of  second  dorsal. 

Inferiorly  the  canal  is  bounded  by  the  pedicle  of  the  second 
dorsal.  Therefore  the  body  of  the  second  dorsal  is  no  longer 
an  anterior  boundary.  These  are  the  only  changes  in  the  bony 
boundaries.  We  still  consider  this  plate  as  in  the  spinal  canal 
for  it  cannot  be  considered  as  in  the  intervertebral  foramen 
until  it  is  entirely  surrounded  by  bone. 

We  note  the  following  bony  changes : 

1.  The  pedicle  of  second  dorsal  appears. 

2.  The  superior  part  of  canal  is  smaller  in  diameter. 

3.  The  body  of  first  dorsal  is  smaller  in  an  antero-posterior 
diameter. 

4.  The  articular  processes  are  larger. 

In  other  words  there  is  a  continuation  of  practically  all 
the  changes  that  were  spoken  of  in  the  foramen  plate.  The 
interarticular  ligament  is  practically  the  same  as  in  the  former 
plate. 

50 


PLATE    7    (Section    31) 


51 


A  right  lateral  view  of  the  spinal  canal  and  its  adjacent 
bony  boundaries,  opposite  the  right  first  dorsal  intervertebral 
foramen,  immediately  external  to  Plate  6. 


A — Foreign  particles. 

B — Posterior      root      of      spinal 

(spinal   ganglion). 
C— Blood   vessel. 
D — Capsular  ligament. 
K — Articular    cartilages. 
F — Blood   vessel. 
G— Fat   cells. 


H— Blood  vessel. 
I— Voluntary   muscle 
T— Blood  vessel. 
K — Vacant  spaces. 
L, — Filaments      of      anterior 

spinal    nerve. 
M — Fatty-fibrous  tissue. 
N— Blood   vessel. 
O — Articular    cartilages. 
P — Fatty-fibrous    tissue. 
Q — Articular   cartilages. 


DESCRIPTION   OF   PLATE  7  53 

The  Articular  Cartilage  on  Bony  Boundaries 

Similar  to  the  former  plates  (See  Plate  5) 

The  Contents  of  Spinal  Canal 

1.  Nervous  Structures.  4.     Fibrous  Tissue. 

2.  Fat  Cells.  5.     Vacant  Spaces. 

3.  Blood  Vessels.  6.     Foreign  Particle. 

They  are  the  same  as  in  the  former  plates  except  that  the 
unknown  particle  has  disappeared. 

1.  Nervous  Structures. 

Anterior  and  posterior  roots  (spinal  ganglion  on  posterior 
root). 

The  roots  have  almost  fused.  The  inferior  filament  of 
the  anterior  root  is  more  closely  associated  with  the  pos- 
terior root  than  the  superior  filament.  A  few  nerve  cells  are 
still  present  in  the  posterior  root  and  part  of  the  epineurium 
of  the  anterior  root  appears  very  loose. 

2.  Fat  Cells. 

(1)  The  canal  is  nearly  filled  with  them. 

(2)  In  the  fibrous  tissue  posterior  to  head  of  rib. 

As  a  whole  they  are  less  in  number.  There  are  none  in 
the  fibrous  tissue  which  separates  the  roots,  but  there  are 
some  infiltrating  the  fibrous  tissues  posterior  to  the  head  of 
the  rib. 

3.  Blood  Vessels. 

(1)  Two  large  ones  inferior  to  nervous  structures   (dis- 
tended). 

(2)  A  small  one  in  capsular  ligament  (collapsed). 


54  THE   INTERVERTEBRAL   FORAMEN 

(3)  Two  posterior  to  body  of  first  dorsal,  one  fair  size, 
the  other  small  (both  distended). 

The  large  distended  vessel  of  the  former  plate  has  bifur- 
cated into  two  vessels.  The  more  posterior  of  these  vessels 
apparently  receives  the  vessel  formerly  seen  in  the  capsular 
ligament  for  this  has  disappeared.  The  vessel  which  was 
situated  anterior  to  the  inferior  articular  process  and  capsular 
ligament  has  descended  still  further  and  is  now  entirely  in 
the  anterior  part  of  the  ligament.  The  vessel  posterior  to 
the  body  of  the  first  dorsal  has  a  very  small  vessel  accom- 
panying it,  which,  no  doubt,  is  derived  from  it. 

4.  Fibrous  Tissue. 

(1)  The  capsular  ligament  (dense). 

(2)  Posterior  to  head  of  rib  (infiltrated  with  fat). 

(3)  Uniting  anterior  and  posterior  roots. 

The  capsular  ligament  is  still  more  prominent.  The  tissue 
posterior  to  the  rib  is  thicker.  Very  little  tissue  unites  the 
roots. 

5.  Vacant  Spaces. 

(1)  Anterior  to  anterior  root. 

(2)  Superior  to  posterior  root. 

6.  Foreign  Particles. 

In  the  superior  part  of  canal. 

These  are  still  further  reduced  in  number. 


DESCRIPTION  OF  PLATE  8   (Section  29) 

This  shows  the  spinal  canal  and  its  adjacent  bony  boun- 
daries external  to  Plate  No.  7. 

The  Bony  Boundaries  of  Spinal  Canal 

Similar  to  the  former  plate  (Plate  7) 

The  pedicle  of  the  second  dorsal  has  fully  formed.  The 
canal  has  been  further  reduced  in  size  and  the  intervertebral 
foramen  is  almost  formed,  the  deficiency  being  in  the  pedicle 
of  the  first  dorsal  above.  In  fact,  this  plate  could  be  con- 
sidered as  in  the  intervertebral  foramen. 

The  bony  boundaries  show  the  following  changes  as  com- 
pared with  the  former  plate: 

1.  The  pedicle  of  second  dorsal  is  larger. 

2.  The  superior  part  of  foramen  is  smaller. 

3.  The  body  of  first  dorsal  is  smaller  in  an  antero-posterior 
diameter. 

4.  The  articular  processes  are  larger. 

5.  The  pedicle  of  first  dorsal  is  beginning  to  form. 

The  Articular  Cartilage  on  Bony  Boundaries 

Similar  to  the  former  plates  (see  Plate  5) 

The  Contents  of  Spinal  Canal 

Similar  to  the  former  plate  (Plate  7) 

1.    Nervous  Structures. 

The  spinal  nerve. 

The  roots  have  practically  fused  and  the  nerve  has  been 
formed.  It  is  oval  in  shape,  situated  obliquely  in  the  canal 

55 


56  THE   INTER  VERTEBRAL   FORAMEN 

and  surrounded  by  fat  cells  and  vacant  spaces.  A  little  loose 
fibrous  tissue  is  attached  to  the  epineurium  at  its  antero- 
superior  part.  Nerve  cells  are  present  in  its  posterior  part 
which  is  the  situation  where  the  spinal  ganglion  was  formerly 
seen.  Evidently,  nerve  cells  are  not  confined  solely  to  the 
ganglion. 

2.  Fat  Cells. 

(1)  The  canal  is  nearly  filled  with  them. 

(2)  In  the  fibrous  tissue  posterior  to  the  head  of  rib. 
There  are  more  in  the  fibrous  tissue  posterior  to  the  head 

of  rib  than  before,  but,  as  a  whole,  they  are  fewer  in  number. 

3.  Blood  Vessels. 

(1)  Two  large  ones  inferior  to  nerve   (distended). 

(2)  A  small  one  in  capsular  ligament   (collapsed). 

(3)  Two  posterior  to  body  of  first  dorsal,  one  fair  size, 
the  other  small  (both  distended). 

The  vessels  appear  about  the  same  except  that  the  wall 
which  separates  the  two  large  ones  is  thicker. 

4.  Fibrous  Tissue. 

(1)  The  capsular  ligament  (dense). 

(2)  Posterior  to  head  of  rib  (infiltrated  with  fat). 

(3)  Attached  to  antero-superior  part  of  nerve  (fine). 

It  is  increased  in  amount.  Posterior  to  the  head  of  the  rib 
it  is  thicker.  A  little  loose  tissue  is  attached  at  the  antero- 
superior  part  of  the  nerve. 

5.  Vacant  Spaces. 

(1)  Anterior  to  nerve. 

(2)  Superior  to  nerve. 

6.  Foreign  Particles. 

In  the  superior  part  of  canal. 
Only  a  very  few  particles  remain. 


LIBRARY  OF 
COLLEGE  -''pr-T 

PHY5 
PLATE  8  (Section  29) 


A  right  lateral  view  of  the  spinal  canal  and  its  adjacent 
bony  boundaries,  immediately  internal  to  the  right  first  dorsal 
intervertebral  foramen  and  immediately  external  to  Plate  7.* 


A — Foreign  particles. 

B— Fat  cells. 

C — Blood   vessel. 

D — Capsular    ligament. 

E — Articular    cartilages. 

F — Blood   vessels. 


G— Voluntary    muscle. 
H — Blood  vessels. 

I — Fibrous  tissue    (fine). 

T — Vacant  spaces. 
K — Articular   cartilages. 
L — Fatty-fibrous   tissue. 
M — Articular  cartilages. 


*This  plate  is  so  close  to  the   intervertebral   foramen  that 
sidered  as  in  the  most   internal  part  of  the   foramen. 


Duld  almost  be  con- 


^3J  !00 


DESCRIPTION  OF  PLATE  9  (Section  26) 

This  shows  the  right  first  dorsal  intervertebral  foramen, 
and  its  adjacent  bony  boundaries. 

The  Bony  Boundaries  of  Intervertebral  Foramen 

.         .       (  Body  of  first  dorsal  (above). 
>F  {  Head  of  second  rib  (below). 

/Inferior  articular  process  of  first  dorsal   (above). 
Superior  articular  process  of  second  dorsal   (be- 
|^      low). 

Superior  j  Pedicle  of  first  dorsal. 
Inferior    j  Pedicle  of  second  dorsal. 

Being  in  the  intervertebral  foramen  it  is  entirely  sur- 
rounded by  bone.  Therefore,  the  pedicle  of  the  first  dorsal 
is  seen  in  addition  to  the  parts  in  the  former  plate.  This 
plate  has  the  same  boundaries  as  given  under  Plate  3,  which 
is  a  drawing  from  this.  The  body  of  the  first  dorsal  is  still 
further  reduced  in  an  antero-posterior  diameter  and  appears 
quite  thin. 

The  Articular  Cartilage  on  Bony  Boundaries 

Similar  to  the  former  plates  (see  Plate  5) 
These  are  well  shown  in  Plate  3. 

The  Contents  of  Intervertebral  Foramen 

1.  Nervous  Structures.  4.     Fibrous  Tissue. 

2.  Fat  Cells.  5.     Vacant  Spaces. 

3.  Blood  Vessels. 

They  are  similar  to  the  former  plate  except  that  the  foreign 
59 


60  THE   INTERVERTEBRAL   FORAMEN 

particles  have  entirely  disappeared.  The  foramen  is  some- 
what quadrilateral  in  shape. 

1.  Nervous  Structures. 

The  spinal  nerve. 

Its  general  shape  and  size  are  shown  very  well  in  Plate 
3.  A  brief  description  of  it  is  also  given  in  connection  with 
the  above  plate.  The  nerve  is  surrounded  by  fat  cells  and 
vacant  spaces.  The  capsular  ligament  is  now  in  contact  with 
it  slightly  postero-inferiorly  and  some  loose  fibrous  tissue  is 
seen  attached  antero-superiorly.  Nerve  cells  remain  present 
in  its  posterior  part. 

2.  Fat  Cells. 

(1)  Postero-superior  to  nerve. 

(2)  Inferior  to  nerve. 

(3)  In  the  fibrous  tissue  posterior  to  head  of  rib. 
They  are  markedly  reduced  in  number  on  account  of  being 

in  the  intervertebral  foramen.  Next  to  the  nerve  they  occupy 
the  most  space.  The  fat  cells  in  the  fibrous  tissue  posterior 
to  the  head  of  the  rib  have  further  increased  in  number. 

3.  Blood  Vessels. 

(1)  Four  fair  sized  ones  in  fibrous  tissue  inferior  to  the 
nerve  (all  distended). 

(2)  A  small  one  in  capsular  ligament  (collapsed). 

(3)  Three  of  fair  size  inferior  to  pedicle  of  first  dorsal 
(all  distended). 

The  two  large  vessels  seen  in  the  former  plate  have  further 
divided  into  four.  They  appear  imbedded  in  fibrous  tissue 
inferior  to  the  nerve.  The  two  vessels  situated  posterior  to 
the  body  of  the  first  dorsal  in  the  former  plate,  are  now  three 
in  number  and  are  seen  passing  beneath  the  pedicle  of  the 
first  dorsal. 


PLATE    9    (Section    26) 


61 


A  right  lateral  view  of  the  right  first  dorsal  intervertebral 
foramen  and  its  adjacent  bony  boundaries.  It  is,  of  course, 
external  to  Plate  8,  which  was  in  the  spinal  canal. 


A— Fat  cells. 

B — Vacant  space. 

C — Capsular    ligament. 

D— Blood   vessel. 

E — Articular    cartilages. 

F— Fat  cells. 

G — Blood  vessel. 


II — Blood  vessels. 

I — Fibrous    tissue    (loosely    arranged). 
T — Thickened   periosteum. 
K — Vacant   space. 
L — Blood   vessel. 
M — Articular   cartilages. 
N— Blood  vessels. 
O — Fatty-fibrous   tissue. 
P — Fibrous  tissue    (dense). 


DESCRIPTION   OF   PLATE  9  63 

4.  Fibrous  Tissue. 

(1)  The  capsular  ligament   (dense). 

(2)  Posterior  to  head  of  rib  (greatly  infiltrated  with  fat). 

(3)  The    thickened    periosteum    of    posterior   surface    of 
first  dorsal   (dense). 

(4)  Attached  to  antero-superior  part  of  nerve  (fine). 

(5)  Inferior  to  nerve  in    which    vessels    are    imbedded 
(dense). 

It  is  more  abundant.  The  capsular  ligament  is  thicker. 
The  tissue  posterior  to  the  head  of  rib  and  the  periosteum 
posterior  to  the  body  of  the  first  dorsal  is  more  abundant. 
The  increased  thickness  of  the  periosteum  is  probably  due  to 
the  thinness  of  the  bone  here.  The  fibrous  coats  of  the  blood 
vessels  inferior  to  the  nerve  are  so  thick  that  it  appears  as  if 
they  were  embedded  in  this  tissue.  This  same  fibrous  tissue 
is  continuous  with  the  capsular  ligament  posteriorly  and  the 
thickened  periosteum  anteriorly.  It  is  also  attached  to  the 
pedicle  of  the  second  dorsal. 

5.  Vacant  Spaces. 

(1)  Anterior  to  nerve. 

(2)  Superior  to  nerve. 


DESCRIPTION   OF  PLATE   10    (Section   24) 

This  is  immediately  external  to  the  right  first  dorsal  inter- 
vertebral  foramen. 

The  Bony  Boundaries  External  to  Intervertebral  Foramen 

(  Part  of  body  of  first  dorsal  (above). 
(Head  of  second  rib  (below). 

{Inferior  articular  process  of  first  dorsal   (above). 
Superior  articular  process   of  second  dorsal    (be- 
low). 

Superior    j  Pedicle  of  first  dorsal. 
Inferior      J  Pedicle  of  second  dorsal. 

(In  this  and  all  the  following  plates,  the  positions  of  the 
bony  boundaries  are  named  according  to  their  relations  to  the 
nervous  structures.) 

The  boundaries  are  very  similar  to  those  of  the  former 
plate,  except  that  a  small  part  of  the  body  of  the  first  dorsal 
which  helped  form  the  anterior  boundary  of  the  foramen,  has 
disappeared.  Therefore,  this  is  not  a  complete  foramen.  This 
plate  bears  the  same  relation  to  the  intervertebral  foramen  as 
Plate  8 ;  both  could  be  considered  as  in  the  foramen. 

The  deficiency  of  the  body  of  the  first  dorsal  is  made  up 
by  fibrous  tissue  and  fat  cells.  The  fibrous  tissue  on  the 
anterior  and  posterior  surfaces  of  the  body  of  the  first  dorsal 
supplies  the  necessary  tissue  here.  From  the  fat  cells  anterior 
to  the  body  of  the  same  vertebra  are  derived  the  necessary 
cells.  A  break  in  the  continuity  of  the  pedicle  of  the  second 
dorsal  is  noted.  This  is  due  to  a  nutrient  foramen  in  this 
situation.  This  foramen  leads  into  the  cancellous  bone  of  the 
pedicle  and  nourishes  it,  conveying  blood  from  one  of  the  large 
vessels  situated  in  the  fibrous  tissue,  inferior  to  the  nerve. 


PLATE   10    (Section   24) 


65 


A  right  lateral  view  immediately  external  to  the  right  first 
dorsal  intervertebral  foramen.* 


A — Blood   vessels. 
B — -Vacant   space. 
C— Fat  ceils. 
D — Vacant   space. 
E — Capsular    ligament. 
p — Blood    vessel. 
G — Articular    cartilages. 
H— Fat   cells. 
I — Nutrient    foramen. 


J — Voluntary   muscle. 

K — Fibrous    tissue    (loosely    arranged). 

L — Vacant    space. 

M — Fibrous  tissue  (dense). 

N— Fat  cells. 

O — Blood   vessel. 

P — Articular    cartilage. 

Q — Fat  cells. 

R — Blood    vessels. 

S- — Voluntary  muscle. 

T — Articular    cartilages. 


*Thia    plate    is    so    close    to    the    intervertebral    foramen     that    it    could    almost    be 
isidered  as  in  the  most  external  part  of  the  foramen. 


DESCRIPTION   OF   PLATE   10  67 

These  nutrient  foramina  are  frequently  noticed  in  the  pedicles 
of  the  upper  dorsal  vertebrae. 

The  Articular  Cartilage  on  Bony  Boundaries 

Similar  to  the  former  plates  (see  Plate  5) 

The  Tissues  External  to  Intervertebral  Foramen 

1.  Nervous  Structures.  4.     Fibrous  Tissue. 

2.  Fat  Cells.  5.     Vacant  Spaces. 

3.  Blood  Vessels.  6.     Voluntary  Muscle. 

They  are  similar  to  the  former  plate  except  for  the  addi- 
tion of  voluntary  muscle. 

1.  Nervous  Structures. 
The   spinal   nerve. 

It  resembles  the  former  plate,  except  that  the  fibrous  tissue 
in  contact  with  it  antero-superiorly  is  more  abundant. 

2.  Fat  Cells. 

(1)  Postero-superior  to  nerve. 

(2)  Inferior  to  nerve. 

(3)  Posterior  to  head  of  rib. 

(4)  In  the  position  formerly  occupied  by  body  of  first 
dorsal. 

(5)  In  the  fibrous  tissue  inferior  to  nerve. 

There  is  more  fat  posterior  to  the  head  of  the  rib.  A  con- 
siderable amount  is  seen  anterior  to  the  body  of  the  first  dorsal. 
This  helps  to  fill  in  where  the  bone  is  deficient.  Fat  cells  have 
begun  to  infiltrate  the  fibrous  tissue  inferior  to  the  nerve. 
As  a  whole  the  fat  is  less  in  amount. 

3.  Blood  Vessels. 

(1)  Three  fair  sized  ones  in  fibrous   tissue  inferior  to 
nerve  (all  distended). 

(2)  A  small  one  in  capsular  ligament  (collapsed). 


68  THE    INTERVERTEBRAL   FORAMEN 

(3)  Several  fair  sized  small  ones  inferior  to  pedicle  of 
first  dorsal  (all  distended). 

Only  three  are  now  seen  inferior  to  the  nerve.  One  gives 
off  a  branch  which  enters  the  nutrient  foramen  in  the  pedicle 
in  this  situation.  The  vessels  passing  beneath  the  pedicle  of 
the  first  dorsal  have  divided  into  five  and  now  occupy  the 
entire  length  of  the  pedicle. 

4.  Fibrous  Tissue. 

(1)  The  capsular  ligament  (dense). 

(2)  Attached  to  antero-superior  part  of  nerve  (fine). 

(3)  Inferior  to  nerve  in    which    vessels    are    imbedded 
(dense). 

(4)  In  the  position  formerly  occupied  by  body  of  first 
dorsal  (dense). 

The  fibrous  tissue  is  further  increased  in  amount.  That 
which  is  attached  to  the  antero-superior  part  of  the  nerve  is 
more  abundant.  The  tissue  which  helps  to  make  up  the 
deficiency  of  the  body  of  the  first  dorsal  replaces  the  thickened 
periosteum  in  this  situation.  Part  of  it  appears  folded  on 
itself  due  to  faulty  technic.  The  fibrous  tissue  posterior  to 
the  head  of  the  rib,  as  seen  in  the  former  plates,  is  entirely 
replaced  by  fat  cells. 

5.  Vacant  Spaces. 

(1)  Anterior  to  nerve. 

(2)  Two  superior  to  nerve. 

6.  Voluntary  Muscle. 

In  the  fibrous  tissue  posterior  to  head  of  rib. 

This  muscle  is  made  up  of  a  small  group  of  fibers,  closely 
collected  together  and  surrounded  by  fibrous  tissue.  They 
are  not  attached  to  bone.  Under  high  magnification  they 
appear  striated,  hence  are  voluntary.  Passing  externally,  the 
muscle  steadily  increases  in  amount. 


DESCRIPTION   OF   PLATE   11    (Section  22^) 

This  is  external  to  the  right  first  dorsal  intervertebral  fora- 
men, external  to  Plate  10. 


The  Bony  Boundaries  External  to  Intervertebral  Foramen 

Anterior    J  Head  of  second  rib. 

{Inferior  articular  process  of  first  dorsal  (above). 
Superior  articular  process   of  second  dorsal   (be- 
low). 

Superior     J  Pedicle  of  first  dorsal. 
Inferior      j  Pedicle  of  second  dorsal. 

The  boundaries  are  very  similar  to  those  of  the  former 
plate,  except  that  that  portion  of  the  body  of  the  first  dorsal 
which  helped  form  the  anterior  boundary  has  entirely  dis- 
appeared. It  is  replaced  principally  by  fibrous  tissue.  The 
nutrient  foramen  is  present  in  the  pedicle  of  the  second  dorsal. 

The  Articular  Cartilages  on  Bony  Boundaries 

1.  Inferior  articular  process  of  first  dorsal. 

2.  Superior  articular  process  of  second  dorsal. 

3.  Body  of  second  dorsal. 

4.  Head  of  second  rib. 

On  account  of  the  body  of  the  first  dorsal  no  longer  being 
present,  the  cartilage  on  it  and  on  that  part  of  the  head  of  the 
rib,  with  which  it  articulates,  is  no  longer  seen.  The  other 
bones  have  cartilage  as  in  the  former  plates. 


70  THE    INTERVERTEBRAL   FORAMEN 

The  Tissues  External  to  Intervertebral  Foramen 

Similar  to  the  former  plate  (Plate  10) 

1.  Nervous  Structures. 
The  spinal  nerve. 

It  appears  somewhat  closer  to  the  pedicle  of  the  first  dorsal, 
otherwise  there  is  no  change. 

2.  Fat  Cells. 

(1)  Posterior-superior  to  nerve. 

(2)  Inferior  to  nerve. 

(3)  Posterior  to  head  of  rib. 

(4)  In  position  formerly  occupied  by  body  of  first  dorsal. 

(5)  In  fibrous  tissue  inferior  to  nerve. 
There  are  no  changes  worthy  of  mention. 

3.  Blood  Vessels. 

(1)  Two  large  ones  in  the  fibrous  tissue  inferior  to  nerve 
(distended). 

(2)  A  small  one  in  capsular  ligament  (collapsed). 

(3)  Several  fair  sized  and  small  ones  inferior  to  pedicle 
of  first  dorsal  (all  distended). 

These  vessels,  which  pass  inferior  to  the  pedicle  of  the  first 
dorsal,  now  seem  so  numerous  that  they  reach  around  and 
become  continuous  with  the  blood  vessel  in  the  capsular  liga- 
ment. The  large  vessels  in  the  fibrous  tissue  inferior  to  the 
nerve  are  reduced  to  two,  neither  of  which  appears  to  enter 
the  nutrient  foramen  in  the  pedicle  of  the  second  dorsal. 

4.  Fibrous  Tissue. 

(1)  The  capsular  ligament  (dense). 

(2)  Attached  to  antero-superior  part  of  nerve  (fine). 

(3)  Inferior  to    nerve    in    which    vessels    are    imbedded 
(dense). 


PLATE   11    (Section   22^) 


71 


A    right    lateral    view    external    to    the    right    first    dorsal 
intervertebral    foramen    immediately    external    to    Plate    10. 


A — Blood   vessels. 

B — Vacant   space. 

C — Capsular    ligament. 

D — Blood  vessel. 

E — Articular    cartilages. 

F — Fat   cells. 

G — Blood   vessel. 

H — Nutrient    foramen. 


I — Blood    vessels. 

J — Fibrous  tissue   (loose). 

K — Fibrous    tissue    (dense). 

L — Vacant   space. 

M — Blood   vessel. 

N — Fatty-fibrous   tissue. 

O — Voluntary   muscle. 

P — Voluntary    muscle. 

Q — Articular   cartilages. 


DESCRIPTION   OF  PLATE  11  73 

(4)  In  the  position  formerly  occupied  by  body  of  first 
dorsal  (dense). 

Fibrous  tissue  almost  entirely  fills  the  position  formerly 
occupied  by  the  body  of  the  first  dorsal.  This  tissue  is  con- 
tinuous with  the  fibrous  tissue  inferior  to  the  nerve  in  which 
the  blood  vessels  are  embedded.  Like  in  the  former  plate, 
this  latter  tissue  is  continuous  with  the  capsular  ligament 
which  now  appears  thicker. 

5.  Vacant  Spaces. 

(1)  Anterior  and  inferior  to  nerve. 

(2)  Superior  to  nerve. 

6.  Voluntary  Muscle. 

(1)  Attached  to  posterior  surface  of  head  of  rib. 

(2)  In  the  fatty-fibrous  tissue  anterior  to  body  of  second 
dorsal. 

It  is  increased  in  amount. 


DESCRIPTION   OF   PLATE   12    (Section  21) 

This  is  external  to  the  right  first  dorsal  intervertebral  fora- 
men, external  to  Plate  11. 

The  Bony  Boundaries  External  to  Intervertebral  Foramen 

C Inferior  articular  process  of  first  dorsal   (above). 
Posterior  J  Superior  articular  process  of  second   dorsal    (be- 
L     low). 

Superior      J  Pedicle  of  first  dorsal. 

.  (  Neck  of  second  rib  (in  front). 

|  Posterior  part  of  pedicle  of  second  dorsal  (behind). 

The  neck  of  the  second  rib  replaces  the  head  of  this  same 
bone.  This  is  explained  as  follows :  The  neck  of  the  rib  is 
continuous  with  the  head,  but  is  on  a  more  external  level ; 
it  is  only  natural  since  we  are  passing  externally  that  the  neck 
of  the  rib  replace  the  head.  The  reason  that  the  neck  is  seen 
more  inferior  to  the  nerve  is  because  the  rib,  from  its  articula- 
tion with  the  bodies  of  the  first  and  second  dorsal  vertebrae, 
passes  inferiorly,  posteriorly  and  externally.  It  must  pass  in 
these  directions  because  it  also  articulates  (the  second  rib) 
with  the  transverse  process  of  the  second  dorsal.  The  anterior 
part  of  the  pedicle  of  the  second  dorsal  has  disappeared,  and 
this  accounts  for  the  space  seen  between  the  posterior  part 
of  the  pedicle  and  the  neck  of  the  rib.  This  space  is  filled  with 
fat  cells,  voluntary  muscle,  and  fibrous  tissue.  This  latter 
tissue  connects  the  posterior  part  of  the  pedicle  with  the  pos- 
terior surface  of  the  neck  of  the  rib.  The  reason  for  the  above 
change  in  the  pedicle  is  that  it  runs  posterior  and  external 
from  the  body  of  the  vertebra.  Therefore,  in  passing  ex- 
ternally, the  anterior  part  of  the  pedicle  is  the  first  to  dis- 
appear. The  nutrient  foramen  in  this  pedicle  still  remains. 

74 


PLATE   12    (Section   21) 


75 


A  right  lateral  view  external  to  the  right  first  dorsal  inter- 
vertebral    foramen,    immediately    external    to    Plate    11. 


A — Blood  vessel. 

B — Vacant    space. 

C— Fat   cells. 

D — Blood    vessel. 

E — Articular    cartilages. 

F — Capsular   ligament. 

G — Blood   vessel. 

H — Nutrient    foramen. 


I — Blood    vessels. 
J — Fibrous   tissue    (loose). 
K — Fibrous    tissue    (dense). 
L — \7acant   space. 
M — Blood   vessel. 
N — Fatty-fibrous  tissue. 
O — Voluntary   muscle. 
P — Fibrous    tissue    (dense). 


DESCRIPTION   OF   PLATE   12  77 

The  Articular  Cartilages  on  Bony  Boundaries 

1.  Inferior  articular  process  of  first  dorsal. 

2.  Superior  articular  process  of  second  dorsal. 

The  neck  of  the  second  rib  is  not  in  bony  contact  with  any 
of  the  adjacent  parts,  hence  no  cartilage  is  seen  on  it.  The 
body  of  the  second  dorsal  has  disappeared,  so  the  cartilage 
present  on  it  in  the  former  plates  is,  of  course,  absent. 

The  Tissues  External  to  Intervertebral  Foramen. 
Similar  to  the  former  plate  (see  Plate  10) 

1.  Nervous  Structures. 
The  spinal  nerve. 

It  is  the  same  as  in  the  former  plate,  except  for  a  slight 
change  in  the  contour. 

2.  Fat  Cells. 

(1)  Posterior-superior  to  nerve. 

(2)  Inferior  to  nerve. 

(3)  Posterior  to  neck  of  rib. 

(4)  In  position  formerly  occupied  by  body  of  first  dorsal. 

(5)  In  the  fibrous  tissue  inferior  to  nerve. 
They  are  the  same  as  in  the  former  plate. 

3.  Blood  Vessels. 

(1)  Two   large   ones    in    fatty-fibrous    inferior   to   nerve 
(distended). 

(2)  A  small  one  in  capsular  ligament  (collapsed). 

(3)  Several  fair  sized  and  small  ones  inferior  to  pedicle 
of  first  dorsal  (all  distended). 

They  are  the  same  as  in  the  former  plate. 


78  THE    INTERVERTEBRAL   FORAMEN 

4.  Fibrous  Tissue. 

(1)  The  capsular  ligament  (dense). 

(2)  Attached  to  antero-superior  part  of  nerve  (fine). 

(3)  Inferior  to  nerve  in  which  the  large  vessels  are  im- 
bedded (dense). 

(4)  In  the  position  formerly  occupied  by  body  of  first 
dorsal  (dense). 

(5)  Connecting  neck  of  rib  with  pedicle  of  second  dorsal 
(dense). 

The  only  change  is  (5). 

5.  Vacant  Spaces. 

(1)  Anterior  and  inferior  to  nerve. 

(2)  Superior  to  nerve. 

6.  Voluntary  Muscle. 

(1)  Attached  to  posterior  surface  of  neck  of  rib. 

(2)  In  the  fatty-fibrous  tissue  anterior  to  pedicle  of  second 
dorsal  and  partly  attached  to  it. 

It  is  increased  in  amount. 


DESCRIPTION   OF   PLATE   13    (Section   19) 

This  is  external  to  the  right  first  dorsal  intervertebral  fora- 
men, external  to  Plate  12. 

The  Bony  Boundaries  External  to  Intervertebral  Foramen 

Similar  to  the  former  plate  (Plate  12) 

There  is  a  larger  space  between  the  posterior  part  of  the 
pedicle  of  the  second  dorsal  and  posterior  surface  of  neck  of 
second  rib.  The  fibrous  tissue  uniting  these  parts  has  dis- 
appeared. 

The  Articular  Cartilage  on  Bony  Boundaries 

Similar  to  the  former  plate  (Plate  12) 

The  Tissues  External  to  Intervertebral  Foramen 

Similar  to  the  former  plate  (see  Plate  10) 

1.  Nervous  Structures. 
The  spinal  nerve. 

It  remains  surrounded  by  fat  cells,  vacant  spaces,  and 
fibrous  tissue.  It  is  in  slight  contact  with  the  capsular  liga- 
ment posteriorly,  but  appears  separated  from  it  on  account 
of  the  blood  vessel  in  the  ligament  being  distended.  Little 
fibrous  tissue  is  attached  to  it  at  its  antero-superior  part,  but 
a  considerable  amount  is  attached  at  its  antero-inferior  part. 
This  latter  tissue  is  derived  from  the  fibrous  tissue  seen  inferior 
to  the  nerve  in  the  former  plates  and  which  has  been  steadily 
approaching  it.  Nerve  cells  still  remain  in  the  posterior  part 
of  the  nerve. 

2.  Fat  Cells. 

(1)  Posterior-superior  to  nerve. 

(2)  Inferior  to  nerve. 

(3)  Posterior  to  neck  of  rib. 

(4)  In  position  formerly  occupied  by  body  of  first  dorsal. 

79 


80  THE   INTERVERTEBRAL  FORAMEN 

(5)  In  the  fibrous  tissue  inferior  to  nerve. 

(6)  In  the  capsular  ligament. 

The  fat  cells  in  the  fibrous  tissue  inferior  to  the  nerve  have 
greatly  increased.  The  only  other  change  is  the  infiltration 
of  fat  cells  into  the  capsular  ligament. 

3.  Blood  Vessels. 

(1)  Two  fair  sized  ones  in  the  fatty-fibrous  tissue  inferior 
to  nerve   (distended). 

(2)  A  fair  sized  one  in  the  capsular  ligament  (distended). 

(3)  Several  fair  sized  and  small  ones  inferior  to  pedicle 
of  first  dorsal  (distended). 

The  vessels  inferior  to  the  nerve  are  smaller,  those  inferior 
to  the  pedicle  of  first  dorsal  seem  to  be  less  in  number  and 
empty  into  the  vessel  in  the  capsular  ligament  or  vica  versa. 

4.  Fibrous  Tissue. 

(1)  The  capsular  ligament  (dense). 

(2)  Inferior  to  nerve    (attached  to  it  at  one  place)    in 
which  some  vessels  are  imbedded  (dense). 

(3)  In  position  formerly  occupied  by  body  of  first  dorsal 
(dense). 

The  tissue  attached  to  the  antero-superior  part  of  the  nerve 
and  that  connecting  the  pedicle  of  second  dorsal  with  neck  of 
rib  has  disappeared.  The  capsular  ligament  is  thicker.  The 
tissue  in  the  position  formerly  occupied  by  the  body  of  first 
dorsal  is  less  abundant. 

5.  Vacant  Spaces. 

(1)  Inferior  to  nerve. 

(2)  Superior  to  nerve. 

6.  Voluntary  Muscle. 

Between  neck  of  rib  and  pedicle  of  second  dorsal. 
It  is  further  increased  in  amount.     It  appears  to  replace 
the  fibrous  tissue  connecting  the  above  parts. 


PLATE    13    (Section   19) 


81 


A  right  lateral  view  external  to  the  right  first  dorsal  inter- 
vertebral  foramen,  immediately  external  to  Plate  12. 


A — Blood  vessel. 

B — Vacant   space. 

C — Capsular    ligament. 

D— Blood   vessel. 

F, — Articular    cartilages. 

F— Fat  cells. 


G — Fibrous    tissue    (dense). 
H — 'Vacant  space. 
I — Blood   vessel. 
T — Fatty-fibrous   tissue. 
K— Blood   vessel. 
L — Voluntary  muscle. 


DESCRIPTION    OF  PLATE   14    (Section   17) 

This  is  external  to  the  right  first  dorsal  intervertebral  fora- 
men, external  to  Plate  13. 

The  Bony  Boundaries  External  to  Intervertebral  Foramen 

,-,          .       (  Transverse  process  of  first  dorsal  (above). 
Posterior  <  _ 

|  Transverse  process  of  second  dorsal   (below). 

Superior  j  Transverse  process  of  first  dorsal. 

.,    .    .        (  Neck  of  second  rib   (in  front). 

1^  Transverse  process  of  second  dorsal   (behind). 

The  reason  for  the  transverse  processes  forming  the  above 
relations  is  because  they  project  externally  from  the  pedicles 
and  articular  processes.  Being  external  to  the  latter  parts, 
it  is  natural  to  find  the  transverse  processes. 

The  Articular  Cartilage  on  Bony  Boundaries 

This  has  entirely  disappeared.  The  bony  parts  present  do 
not  articulate  with  one  another.  No  cartilage  is  present  in 
any  of  the  remaining  plates. 

The  Tissues  External  to  Intervertebral  Foramen 

Similar  to  the  former  plate  (see  Plate  10) 

1.    Nervous  Structures. 

The  spinal  nerve. 

It  appears  comparatively  free  from  the  surrounding  parts; 
however,  this  is  no  doubt  due  to  faulty  technic.  Posterior 
to  it  a  vacant  space  is  seen  and  the  nerve  is  free.  The  nerve 
evidently  has  been  torn  from  its  connection  with  the  fibrous 
tissue  in  this  situation,  for  it  was  attached  to  it  in  the  former 
plate,  and  is  also  attached  in  the  plates  which  follow.  Anterior 
to  the  nerve  all  tissue  has  disappeared. 

83 


84  THE   INTERVERTEBRAL   FORAMEN 

2.  Fat  Cells. 

(1)  Postero-superior  to  nerve. 

(2)  Inferior  to  nerve. 

(3)  Posterior  and  superior  to  neck  of  rib. 

(4)  In  the  fibrous  tissue  inferior  to  nerve. 

(5)  In  the  fibrous  tissue  between     the    transverse    pro- 
cesses. 

It  is  markedly  noticeable  how  few  fat  cells  are  in  contact 
with  the  nerve. 

3.  Blood  Vessels. 

(1)  One  small  one  in  the  fatty-fibrous  tissue  inferior  to 
nerve  (distended). 

(2)  Two  small  ones  among  the  fat  cells  between  the  trans- 
verse process  of  second  dorsal  and  neck  of  rib   (distended). 

(3)  Several  small  ones  inferior  to  transverse  process  of 
first  dorsal  (distended). 

The  one  which  was  in  the  capsular  ligament  has  dis- 
appeared. The  vessels  in  the  fatty-fibrous  tissue  inferior  to 
the  nerve  are  smaller.  Only  one  of  these  can  now  be  dis- 
tinguished. The  two  vessels  seen  between  the  transverse 
process  of  second  dorsal  and  neck  of  the  rib  have,  no  doubt, 
descended  there  from  the  fatty-fibrous  tissue  seen  inferior  to 
nerve  in  the  former  plate. 

4.  Fibrous  Tissue. 

(1)  Between  the  transverse  processes  (loose). 

(2)  Inferior  to  nerve    (dense). 

(3)  Antero-superior  to  nerve  (dense). 

That  which  was  situated  in  the  position  formerly  occupied 
by  the  body  of  the  first  dorsal  has  disappeared,  except  for  a 
small  amount  which  is  attached  to  the  anterior  part  of  the 
transverse  process  of  the  first  dorsal,  antero-superior  to  the 
nerve.  The  fibrous  tissue  inferior  to  the  nerve  appears 


PLATE   14    (Section   17) 


85 


A  right  lateral  view  external  to  the  right  first  dorsal  inter- 
vertebral  foramen,  immediately  external  to  Plate  13. 


A — Blood    vessels. 

B — Vacant  space. 

C — Fatty-fibrous    tissue. 

D — Fat    cells. 

E — Blood  vessel. 


F — Fibrous   tissue    (dens. 
G — Blood    vessel. 
H — Fatty-fibrous   tissue. 
I — Voluntary    muscle. 


^'-H  ;,,--•' att* 

5\\<}^ 


DESCRIPTION   OF   PLATE   14  87 

greatly  infiltrated  with  fat  cells.     The  fibrous  tissue  between 
the  transverse  processes  replaces  the  capsular  ligament. 

5.  Vacant  Spaces. 

(1)  Posterior  to  nerve. 

(2)  Inferior  to  nerve. 

The  nerve  appears  torn  from  the  surrounding  fibrous  tissue 
both  posteriorly  and  inferiorly. 

6.  Voluntary  Muscle. 

Between  the  transverse  process  of  second  dorsal  and  neck 
of  rib. 

It  is  further  increased  in  amount,  but  remains  in  its  old 
position. 


DESCRIPTION    OF   PLATE   15    (Section    15) 

This  is  external  to  the  right  first  dorsal  intervertebral  fora- 
men, external  to  Plate  14. 

The  Bony  Boundaries  External  to  Intervertebral  Foramen 
Similar  to  the  former  plate  (Plate  14) 

A  nutrient  foramen  is  beginning  to  form  in  the  transverse 
process  of  the  first  dorsal. 

The  Tissues  External  to  Intervertebral  Foramen 

1.  Nervous  Structures.  4.     Fibrous  Tissue. 

2.  Fat  Cells.  5.     Voluntary  Muscle. 

3.  Blood  Vessels. 

The  vacant  spaces  have  disappeared.  This  is  the  only 
change. 

1.     Nervous  Structures. 

(1)  Anterior  and  posterior  primary   divisions   of   spinal 
nerve. 

(2)  White  and  gray  rami  communicantes  of  sympathetic. 
The  spinal  nerve  is  bifurcated  into  a  large  anterior  and 

several  small  posterior  primary  divisions.  The  reasons  for 
the  greater  difference  in  size  of  the  divisions  was  given  in  the 
introduction  (page  18).  A  few  nerve  cells  are  present  in  the 
anterior  division.  Nerve  cells  in  these  plates  appear  in  the 
spinal  ganglion,  spinal  nerve,  and  the  anterior  division  of  the 
nerve.  This  is  not  the  ordinary  arrangement  for  they  are 
usually  entirely  confined  to  the  spinal  ganglion. 

Immediately  above  the  middle  of  the  superior  part  of  the 
anterior  division  of  the  spinal  nerve,  two  nervous  structures 
will  be  noticed.  They  are  either  entering  or  leaving  the  an- 
terior division,  and  are  the  gray  and  white  rami  communi- 


PLATE    15    (Section    15) 


89 


A  right  lateral  view  external  to  the  right  first  dorsal  inter- 
vertebral  foramen,  immediately  external  to  Plate  14. 


A— Blood  vessels. 

B — Fibrous   tissue    (fine). 

C— Blood   vessel. 

D — Fatty-fibrous  tissue. 

E — Posterior       primary       divis 

spinal    nerve. 
F — Fibrous  tissue    (dense). 


C, — Fibrous   tissue   (dense). 
H — White     and     gray     rami     communi- 
cantes    of    sympathetic. 

I — Anterior   primary   division  of  spinal 
nerve. 

T — Fatty-fibrous  tissue. 
K — Blood  vessel. 
L— Fat  cells. 
M— P.lood   vessels. 
X — Voluntary   muscle. 


DESCRIPTION    OF    PLATE   15  91 

cantes  of  the  sympathetic.  They  are  close  together,  separated 
only  by  a  small  amount  of  fibrous  tissue.  Both  are  sur- 
rounded by  a  fibrous  sheath  and  are  similar  in  structure.  It 
would  be  well  to  recall  the  histologic  structure  of  these  parts. 
The  following  is  taken  from  Bailey's  Histology:  "The  fibers 
of  the  white  rami  communicantes  are  mostly  fine  and  medul- 
lated.  The  axones  of  the  sympathetic  cells  [this  would  in- 
clude the  gray  rami]  are  fine  and  non-medullated  or  thinly 
medullated."  From  this,  it  can  be  seen  that  there  is  a  slight 
difference  in  the  histologic  structure  in  these  two  parts.  The 
reason  this  difference  cannot  be  confirmed  in  this  series  is, 
perhaps,  due  to  the  technic  required  to  prepare  this  speci- 
men. The  nitric  acid  used  may  be  responsible. 

The  following  facts  prove  the  above  structures  to  be  the 
white  and  gray  rami  of  the  sympathetics : 

1.  Because  practically  all  authorities  state  that  such  struc- 
tures pass  to  and  away  from  the  anterior  division  of  the  spinal 
nerves  in  the  dorsal  region. 

2.  Because  they  possess    that    fine    histologic    structure 
which  is  said  to  be  characteristic  of  these  parts.     The  cerebro- 
spinal  nerve  fibers  are  coarser. 

3.  Because  they  are  so  close  together.     The  findings  in 
this  respect    agree    with    those    of    Langley.     (See  footnote, 
page  19.) 

All  the  nervous  structures  are  imbedded  in  fibrous  tissue, 
which,  for  the  most  part,  is  fairly  dense,  and  appears  very 
intimately  adherent  to  the  epineurium  of  the  nervous  struc- 
tures. The  epineurium  is  more  firmly  adherent  to  the  sur- 
rounding fibrous  tissue  than  to  the  nerves.  No  other  tissue 
is  in  contact  with  the  nervous  structures. 

2.    Fat  Cells. 

(1)  Posterior  and  superior  to  neck  of  rib. 

(2)  In  the  fibrous  tissue  inferior  to  nervous  structures. 


92  THE   INTER  VERTEBRAL   FORAMEN 

(3)  In  the  fibrous  tissue  between  the  transverse  pro- 
cesses. 

Fat  cells  no  longer  are  in  contact  with  any  of  the  nervous 
structures. 

3.  Bloodvessels. 

(1)  One  small  one    in    fatty-fibrous    tissue    inferior    to 
nervous  structures  (distended). 

(2)  Two  small  ones  among  fat  cells  between  the  trans- 
verse process  of  second  dorsal  and  neck  of  rib  (distended). 

(3)  Several    small    ones    inferior    to    transverse    process 
of  first  dorsal  (distended). 

The  vessels  are  very  similar  to  the  former  plate. 

4.  Fibrous  Tissue. 

(1)  Entirely  surrounding  the  nervous  structures  (dense). 

(2)  Between  the  transverse  processes  (loose). 

This  tissue  has  greatly  increased  in  amount.  One  band  of 
fibrous  tissue  attaches  to  the  transverse  process  of  the  first 
dorsal  posterior  to  the  nervous  structures,  and  passes  down- 
ward and  forward,  behind  the  posterior  division  of  the  nerve 
and  becomes  continuous  with  the  fibrous  tissue  inferior  to 
the  nervous  structures.  The  band  in  this  situation  also  has 
an  attachment  which  connects  it  to  the  transverse  process  of 
the  second  dorsal.  (This  replaces  the  old  capsular  ligament.) 
It  then  passes  inferior  to  the  nervous  structures,  then  anterior 
to  them.  Some  of  this  tissue  passes  superior  to  the  nervous 
structures  and  attaches  to  the  inferior  surface  of  the  trans- 
verse process  of  the  first  dorsal.  (It  is  in  this  fibrous 
tissue  that  the  white  and  gray  rami  are  imbedded.)  The  re- 
maining part  of  it  passes  up  anterior  to  the  transverse  process 
of  the  first  dorsal  to  which  it  is  attached.  The  fibrous  tissue 
appears  broken  here,  which  is,  no  doubt,  due  to  faulty  technic. 


DESCRIPTION    OF   PLATE    15  93 

The  remaining  fibrous  tissue  connects  the  two  transverse  pro- 
cesses posteriorly,  and  in  some  places  is  greatly  infiltrated  with 
fat.  Some  areolar  tissue  is  present  superior  to  the  posterior 
primary  division  of  the  nerve. 

5.    Voluntary  Muscle. 

Between  the  transverse  process  of  second  dorsal  and  neck 
of  rib. 

It  is  further  increased  in  amount,  but  remains  in  its  old 
position. 


DESCRIPTION    OF    PLATE  16    (Section    13) 

This  is  considerably  external  to  the  right  first  dorsal  inter- 
vertebral  foramen,  external  to  Plate  15. 

The  Bony  Boundaries  External  to  Intervertebral  Foramen 
Posterior  J  Transverse  process  of  second  dorsal. 
Superior  j  Transverse  process  of  first  dorsal. 

T    ,    .       f  Neck  of  second  rib  (in  front). 
Inferior  <  _,  ,    .,    ,  .    ,. 

|  Transverse  process  of  second  dorsal  (behind). 

The  transverse  process  of  the  first  dorsal  no  longer  has 
any  part  of  it  posterior  to  the  nervous  structures.  This  is 
the  only  change  in  the  bony  boundaries.  The  nutrient  fora- 
men in  the  above  transverse  processes  is  fully  formed. 

The  Tissues  External  to  the  Intervertebral  Foramen 
Similar  to  the  former  plate  (Plate  15) 

1.    Nervous  Structures. 

(1)  Anterior   and   posterior  primary   divisions   of  spinal 
nerve. 

(2)  White  and  gray  rami  communicantes  of  sympathetic. 
These  are  very  similar  to  the  former  plate.     The  anterior 

and  posterior  divisions  appear  to  be  passing  a  little  more 
anteriorly,  for  the  transverse  process  of  the  first  dorsal  does 
not  cover  them  superiorly  as  much  as  formerly.  The  sym- 
pathetic fibers  are  still  close  together  but  have  passed  anteriorly 
and  inferiorly  and  are  now  imbedded  in  the  fibrous  tissue 
anterior  to  the  anterior  division  of  the  nerve. 


PLATE    16    (Section    13) 


95 


A  right  lateral  view  external  to  the  right  first  dorsal  inter- 
vertebral  foramen,  immediately  external  to  Plate  15. 


A — Blood  vessel. 

B — Fatty-fibrous  tissue. 

C — Posterior    divisions   of   spinal    nerve. 

D — Fibrous    tissue    (dense). 

E — Blood   vessel. 

F — Blood  vessel. 

G — Blood  vessel. 


H— Nutrient  foramen. 

I — Anterior    division    of    spinal    nerve. 

J — White    and    gray    rami    of    sympa- 
thetic. 

K — Blood    vessels. 
L— Fat   cells. 
M — Voluntary   muscle. 


DESCRIPTION   OF   PLATE  16  97 

2.  Fat  Cells. 

(1)  Posterior  and  superior  to  neck  of  rib. 

(2)  In  fibrous  tissue  inferior  to  nervous  structures. 

(3)  In  fibrous  tissue  between  the  transverse  processes. 
They  are  similar  to  the  former  plate. 

3.  Blood  Vessels. 

(1)  One  of  fair  size  and  a  small  one  in  fatty-fibrous  tissue 
inferior  to  nervous  structures   (distended). 

(2)  Two  small  ones  among  the  fat  cells  between  the  trans- 
verse process  of  second  dorsal  and  neck  of  rib  (distended). 

(3)  Several  small  ones  inferior  to  transverse  process  of 
first  dorsal  (distended). 

(4)  One  fair  sized  one  among  the  fat  cells  between  the 
transverse  processes  (distended). 

The  vessel  between  the  transverse  processes  is  a  new  one. 
It  appears  cut  almost  longitudinally.  The  fair  sized  vessel 
inferior  to  the  nervous  structures  is  also  new  and  appears  cut 
nearly  longitudinally.  No  doubt,  both  of  these  vessels  are 
passing  in  this  direction,  hence  are  partly  included  in  this  plate. 

4.  Fibrous  Tissue. 

(1)  Entirely  surrounding  the  nervous  structures  (dense). 

(2)  Between  the  transverse  processes  (loose). 

The  fibrous  tissue  surrounding  the  nervous  structures  ap- 
pears broken  and  is  not  continuous  above  the  anterior  division 
of  the  nerve.  This  is,  no  doubt,  due  to  faulty  technic. 

5.  Voluntary  Muscle. 

Between  the  transverse  process  of  second  dorsal  and  neck 
of  rib. 

It  is  still  further  increased  in  amount,  but  remains  in  its 
old  position. 


SUMMARY 
Nervous  Structures  and  Their  Immediate  Relations 

Anterior  and  Posterior  Roots  (Spinal  Ganglion  on  Pos- 
terior Root).  The  roots  are  located  in  the  spinal  canal  being 
held  together  by  fatty-fibrous  tissue  and  are  entirely  sur- 
rounded by  fat  cells. 

Spinal  Nerve.  The  spinal  nerve  is  formed  by  the  union  of 
the  anterior  and  posterior  roots  in  the  spinal  canal,  or  the  most 
internal  part  of  the  intervertebral  foramen,  and  passes  through 
the  foramen  and  external  to  it,  where  the  nerve  bifurcates. 
In  the  spinal  canal  it  is  entirely  surrounded  by  fat  cells.  In 
the  intervertebral  foramen  it  is  almost  completely  surrounded  by 
fat  cells.  However,  it  is  in  slight  contact  with  the  capsular 
ligament  at  its  postero-inferior  part  and  with  some  loose 
fibrous  tissue  at  its  antero-superior  part.  Outside  of  the 
intervertebral  foramen  the  nerve  is  in  slight  contact  with  the 
capsular  ligament  posteriorly,  with  fibrous  tissue  antero- 
superiorly,  and  further  externally  with  fibrous  tissue  inferiorly. 
In  all  other  parts  it  is  surrounded  by  fat  cells,  except  the 
supero-anterior  portion,  where  the  blood  vessels  which  pass 
inferior  to  the  pedicle  separate  it  from  that  bone. 

Anterior  and  Posterior  Primary  Divisions.  The  spinal 
nerve  bifurcates  into  these  divisions  external  to  the  inter- 
vertebral  foramen.  They  are  completely  surrounded  by  fibrous 
tissue,  which,  for  the  most  part,  is  fairly  dense  and  intimately 
adherent  to  the  epineurium  of  the  nerves.  This  tissue  is  also 
attached  to  the  two  adjacent  transverse  processes.  The  ner- 
vous structures  pass  immediately  inferior  to  the  transverse 
process  of  the  upper  vertebra  and  are  very  close  to  it. 


SUMMARY  99 

White  and  Gray  Kami  Communicantes  of  the  Sympathetic. 
These  leave  the  superior  part  of  the  anterior  primary  division 
of  the  nerve,  therefore  are  external  to  the  intervertebral  fora- 
men. Being  very  closely  associated,  they  emerge  together. 
They  pass  downward,  forward  and  outward,  (inferior,  anterior 
and  external)  anterior  to  the  anterior  division  of  the  nerve 
and  are  imbedded  in  the  fibrous  tissue  in  that  situation.  Each 
ramus  has  its  own  epineurium. 

Thus  we  see  that  fat  serves  as  the  principal  protective 
medium  for  the  nervous  structures  in  the  spinal  canal  and  in- 
tervertebral foramen.  Fibrous  tissue  acts  as  the  main  pro- 
tective agency  external  to  the  foramen. 

Other  Interesting  Facts 

Passing  externally  from  the  spinal  canal  it  is  markedly 
noticed  how  the  fat  tissue  decreases  in  amount.  In  the  spinal 
canal  and  the  intervertebral  foramen,  the  nervous  structures 
were  practically  imbedded  in  this  fat  tissue,  being  in  actual 
contact  with  it.  External  to  the  intervertebral  foramen,  com- 
paratively little  fat  is  seen.  In  Plates  15  and  16,  the  most 
external,  there  are  no  fat  cells  touching  the  nervous  structures. 

Another  easily  detected  change  is  the  increase  in  fibrous 
tissue  passing  externally.  In  the  spinal  canal  there  is  no 
fibrous  tissue  surrounding  the  nerves.  Of  course  the  epineu- 
rium, which  is  of  fibrous  tissue,  is  always  present.  In  the 
intervertebral  foramen  the  fibrous  tissue  begins  to  appear, 
and  outside  of  the  foramen  the  nervous  structures  are  com- 
pletely embedded  in  it.* 

In  order  to  fully  appreciate  the  above,  compare  Plate  5, 
the  most  internal,  with  Plate  16,  the  most  external.  At  a 
glance  this  comparison  shows  how  the  external  fibrous  tissue 

*The  term  fascia  may  be  supplemented  for  the  fibrous  connective  tissue  external 
to  the  intervertebral  foramen. 


100  THE   INTERVERTEBRAL  FORAMEN 

replaces  the  internal  fatty  tissue  as  the  protecting  medium  of 
the  nervous  structures. 

Externally  the  fat  has  a  tendency  to  get  further  away  from 
the  nervous  structures  and  the  fibrous  tissue  closer  to  them. 

Another  interesting  fact  is  the  size  of  the  spinal  nerve  as 
compared  with  the  intervertebral  foramen.  This  is  very  well 
shown  in  Plate  3,  where  the  foramen  is  about  three  times  the 
size  of  the  nerve.  The  intervertebral  disc  between  the  first 
and  second  dorsal  vertebrae  averages  approximately  1  mm.  in 
thickness.  If  the  disc  should  shrink,  the  foramen  would  be 
reduced  in  size,  and  this  reduction  would  be  principally  in  a 
supero-inferior  diameter;  the  pedicles  of  the  two  vertebrae 
tending  to  approach  one  another.  If  it  should  shrink  away 
entirely,  the  foramen  would  be  reduced  from  its  normal  4  mm. 
supero-inferior  diameter  to  about  3  mm.  However,  even  then 
it  would  be  impossible  for  the  nerve  to  be  pinched  by  bone. 

Should  the  articular  cartilages  on  the  articular  processes 
undergo  thinning,  the  foramen  would  be  actually  increased  in 
size.  This  increase  would  be  principally  in  an  antero-posterior 
diameter,  the  distance  between  the  superior  articular  process 
of  the  second  dorsal,  and  the  body  of  the  first  dorsal  being 
increased  on  account  of  the  superior  articular  process  passing 
posteriorly.  The  thickness  of  each  articular  cartilage  on  these 
processes  is  approximately  54  of  a  mm.  If  they  should  both 
undergo  complete  atrophy  the  foramen  would  be  actually  in- 
creased about  y2  a  mm.  in  its  antero-posterior  diameter. 

From  dissection-room  observations,  I  believe  I  am  justified 
in  stating  that  if  any  changes  occur  in  the  size  of  the  inter- 
vertebral discs  or  the  articular  cartilages,  they  have  a  marked 
tendency  to  become  thinner  rather  than  thicker.  Should  both 
the  disc  and  the  articular  cartilages  undergo  thinning  at  the 
same  time,  the  foramen  would  not,  in  all  probability,  be 
decreased  as  much  in  size  as  when  the  disc  itself  is  thinned. 
I  have  seen  many  ankylosed  specimens  where  the  inter- 


SUMMARY  101 

vertebral  foramina  have  been  greatly  reduced  in  size,  but  in 
every  instance  there  seemed  enough  room  for  the  nerve  to 
pass  free  from  any  bony  pressure.  Possibly,  in  some  such 
cases,  the  nerve  may  be  subject  to  actual  bony  pressure,  but 
from  my  observations,  this  occurrence  is  extremely  rare. 

Remember,  the  nervous  structures  in  the  spinal  canal  and 
intervertebral  foramen  are  embedded  in  fat.  This  tissue  in 
the  living  subject  is  in  a  semi-fluid  condition.  Thus  we  see 
that  the  nervous  structures  are  embedded  in  a  semi-fluid  sub- 
stance, one  of  the  body's  best  protective  agencies.  The 
nerves  being  composed  of  such  a  highly  specialized  tissue, 
and  therefore  so  vital,  nature  seems  to  use  every  possible 
precaution  to  protect  them  from  bony  pressure.  This  is  the 
reason,  no  doubt,  that  the  intervertebral  foramina,  in  both 
animal  and  man,  are  so  much  larger  than  the  nerves  them- 
selves. 


Date  Due 


A  000  548  238  5 


WE  725 
S     9721 


c.  1 

Swanberg:  the  interver- 
tebral  foramen 


CCM  LIBRARY 


